It's not like this superficially either. That's literally what the word is.
finite - to have a limit, be bounded
The de- part is acting like it does in words like defraud. It's not a negative, like you might see in detox, where it means to remove something or undo something. Instead, it simply insists something has been done, not unlike the suffix -ify. You've been defrauded. In a manner of speaking, you could say you've been "fraud-ified".
You could say something that has been defined has been "finite-ified". The possibilities of what it could be were limitless, but you restricted them to something specific. You've made it finite. You've defined it. It is definite.
It's more that finite is easier because it has the long I sound at the beginning which clearly designates it as I. The short i sound in most English dialects is a middling kind of "ehh" sound that can be confused for an e a lot when sounding out a word. When I misspell definitely it's because I spell it defenitely.
Me, writing an entire sentence describing process, rules and hierarchy within an organization so that I don't have to try to spell the single word which describes this concept:
steno's not just court, it's still the easiest way to do live tv captioning and CART and such
there's also still a big hobbyist group around it, plover and hobbyist stenoboards have made it pretty easy to get into from that angle instead