Why are many businesses in democratic nations largely undemocratic?

Capitalism is antithetical to democracy. Capitalism left unchecked will eventually lead to fascism.

- The first one is true.
  In democracy, the people rule society
  In capitalism, the rich rule the economy
  The economy always rules society
  In a capitalist democracy, society serves two masters. Both opposites. It's inherently unstable because it's self contradicting.

Because as of yet the means of production aren't public property. So the people who own them get to decide the structure of production and they decided we don't get a say in how they are used.

- A mixture of both, with the public holding primary power. There's benefit to people having a better perspective on that which surrounds them immediately, but as industry gets more complex and advances ever more, that "immediate" shrinks more and more as a proportion of the overall production process.
- Those are so similar to each other in comparison with capitalism that at this stage, we mostly use the same words to describe both.

Should the janitorial staff have equal says as to the executives in how funds should be allocated?
Given their propensity for allocating the funds to themselves, probably.
You can use all of these same arguments to argue against democracy in nations, too. The average person has no idea how the nation works, all of the ins and outs of government, to say nothing of the larger global stage. Clearly what we need is a monarchy!
He wouldn't need to count boxes if the books were shared with the whole company, would he?

Why would you expect them to be?

If my family starts a restaurant and hires additional workers to, for example, help clean, bus tables, wait tables, and so on, I think it would be kinda weird to share the decision making between all employees. It makes more sense for employee owned corpos, but most small businesses have an owner or owners whose main job is steering the business.

It would only seem weird because you are used to it. Not because it is right.
The person "steering the business" should be in that position at the behest of the workers. If you can't run a business literally by yourself, you should share power with the people hired to help as if you would a partner.
- Yeah I just don't agree with you.
  There is certainly a broad set of circumstances where businesses can share ownership between employees, but that does not mean there are not other circumstances where work is done purely in exchange for money, benefits, or both.
  If you and 4 friends want to start a pizza shop, cool do it democratically. If I do a business selling a product all myself and every other Sunday I pay someone to come lick my stamps for an hour so I can spend time with my kids, that person is not an equal partner.
  Edit: to be extra clear, democracy is based on the concept that people are all functionally equals in capability, information, and perspective. Basically that countrymen are homogenous. Inside a specialized enterprise of any kind (especially small ones) this need not be true.
  Edit 2: or if that's insufficient and all businesses must be democratic, then I necessarily must be allowed to hire based on whatever criteria I so choose. Work ethic, want to keep the company aligned with my interests, religion, ability, height, anything. That's the only way to guarantee a homogeneous pool and may also be the democratic will of the group of people who begin the business.
Because I would expect people in democratic nations to value democracy and see it as worth exercising in business. This is in part as I see democracy as a formal way of referring to being open to discussion of opinions and ideas in organizing any group.
Why would you want to be part of any group that may reject open discussion of its organization?
- In a democracy you vote on what happens with a shared resource that belongs to all of you, like a country. If a business has several owners they might steer it democratically, like a family business deciding together what to do. But if that business hires employees, the employees don't vote, because it's not their shared resource, so why would they have power to decide on it?
  Of course that doesn't preclude open discussion. Many businesses decide together with their employees, it's just based on discussion and exchange of ideas, not on voting. Why would you hire an expert and then vote among employees instead of letting the expert decide on their area of expertise?
- Because you can easily swap companies, but you can't easily swap countries.

Depending on who you ask, Capitalist countries aren't truly democratic because of this, and Capital's influence on government.

I'm proud of you for asking a difficult question that you won't get a satisfying answer to.

Its almost like asking "why doesnt everyone share cars?" You probably aren't using one all the time, they're expensive to maintain, why not distribute the load to society and just have fleets of cars you borrow whenever you need one? Like a vehicle library.

Some people will love this idea, it would work very well for them. Some people will hate this idea and rail about how its the death of freedom and personal choice. And some will very rightly wonder "why are we talking about cars? Trains solve this problem 1000x better!"

Privately owned business is a problem, and a major component of the problem is that petite bourgeoisie small business owners believe they're part of the broader "business class" which doesn't exist. They're exploited smallholders who serve the interests of the truly rich and powerful by ideologically aligning with them against workers, whom they universally believe are too stupid, selfish, and myopic to properly make decisions for themselves or anyone else.

why not distribute the load to society and just have fleets of cars you borrow whenever you need one? Like a vehicle library.
There are companies that do this. Zipcar is one I’ve used for short-term car rentals to go get groceries while I was in college.

Because you are not paying enough attention:

a Joint-stock-company is by definition democratic. The shareholders are meeting reguarly and voting who get's to sit on the board, can fire the CEO and so. That doesn't apply to the workers, yes, but between the owners it kind of is democratic.
Yes, I know that many tech companies have this strange divide between "voting stock" and "non-voting stock" and founders, who still are in control without owning the majority of the stock, but that is an american thing and not legal in many parts of the world
there are also many ways to ensure democratic collaboration within a company. Look up the german "Betriebsräte" f.e.
there are also many cooperatives around there who are owned by their workers
and there are many state-owned companies around in democratic nations

"kind of democratic between the owners" is just oligarchy. still not democratic.
- That's like saying the foreigners not having a vote is being not democratic though. Because 100% of the owners have voting rights not only a few.
  I think what you intend to criticize is the fact that owners and "employees" can be separated, right? If yes then I'm with you.
Because you are not paying enough attention:
I appreciate the examples provided but disagree with your opening, and would suggest the same of you. I specifically said "many businesses" and "largely undemocratic" as I was aware of most of the examples you gave beforehand.
In particular I don't view the joint-stock model as sufficiently democratic due to what you already acknowledge, i.e. limited to owners/shareholders.
Regardless, appreciate you bringing to light "Betriebsräte", as I'll have to look into that.
- Democracy is "owned" by stakeholders, and those stakeholders are the people. So it makes sense for them to have a say in how government works.
  A company is owned by shareholders, and they take all of the risk for the company. An employee shows up and gets paid, with none of the downside risk (their paycheck won't go negative), so the employee isn't a stakeholder. Therefore, shareholders make the decisions, not employees.
  In some structures, employees are the share holders and thus help make the decisions.

You get where I was going with this! It's exactly that constructed form, and the supposed favoring of it, that led to my asking this.
If a society claims to embrace democracy, but doesn't extend this to the organization of its businesses, how much do they embrace democratic values?
Violence tends to speed things along.
Just sayin.

What business is run democratically? You might mean an anarcho-syndicalist commune or an autonomous collective.