system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some websites tell you that they use cookies and have a 'got it' button, if almost every website uses cookies?
gpt
The EU made it mandatory for websites in that region to inform users that they're putting a small file on the users computer, that can be used to track that users browsing habit on that and other sites.

Privacy laws are a big thing in Europe, so it was a long thing common. It basically means that you now consent to them doing that, whereas before unless you were tech-savvy, you have no idea. 

If you're not in Europe, and/or browsing a European site, you might still see it, as it's easier to just make it a global site change, than to filter it depending on where the users are coming from. 

tl;dr: EU made it mandatory to tell people they're being tracked by cookies, as most people have absolutely no idea what a cookie even is, much less what they do, and people ought to consent to that kind of thing.