There are still local governments or police forces announcing important things via Twitter. There are still interesting and smart people posting there. There are all those "legacy" accounts which are not active anymore, but have valuable content. Nitter was the last way to read this and this is now lost.
If they were truly smart they wouldn't be on a site run by a narcissistic right wing billionaire with breeding fantasies that's turned it into a fascist echo chamber rife with CSAM, antisemitism, and disinformation.
If Stephen King wants to share his accumulated wisdom for free with millions of readers, hopeful artists, random people on the street who’ve never heard of him, what is the best way to reach them? Start a blog that will never show up in any search results behind the pages of machine-generated SEO junk about how they have answers for “Stephen King blog”, right? Because then he had zero impact but retains the moral high ground.
It's not so simple. A lot of people aren't there because they like Elon Musk, they're there because people they like having discussions with are there. And those people are there for the same reason.
It's sort of like a phone company that doesn't allow customers that are on other phone companies. You have to be on the same phone company as your fiends or you can't call them. You can't change to another phone company because you won't be able to call your friends anymore. You'd be stuck because the phone company owns your ability to connect to other people. They own your contacts list.
Fortunately there's regulations to prevent phone companies from doing this, they are required to interconnect. This means you can change to another phone company, and many places you can keep your phone number, so you can do this without your friends even knowing.
There are no such regulations for social media. So Elon Musk bought people's contact lists on Twitter. People can't change platforms because Elon Musk owns people's ability to connect with other people. And because contacts aren't closed groups (people don't have all the same contacts as each other) it's basically impossible to organize an effort where everyone moves to another platform. That would involve organizing nearly everyone on the platform to do it at the same time. It's not really all that feasible to organize hundreds of millions of people that don't really agree with each other on anything to abandon a platform all at once.
But there's been a steady decline in users since Musk took over. Eventually maybe another platform will reach critical mass and there could be a massive number of people go to that platform. Happened with Myspace, Digg, etc. But really social media platfroms should be required by law to interoperate so if a company is well run there's less of a barrier to entry for another company to step in and take over. But that would be something like free market capitalism, and the heads of corporations don't actually want that despite what they say.
I totally agree on the usefulness of Nitter, but hell, imagine following your police force on social media. Like they don't have enough with oppressing you, they also want to feed you their bullshit.