> Why are captchas even a thing still?

Because it works, to some degree. It keeps away the annoying cheap bots and stupid kids. Smarter or more dedicated actors can still circumvent it, but even they are least slowed down to some degree.

But thinking about, maybe just putting a 20 second pause after which you have to push a button might be already good enough for all this. And every stupid bot avoiding it will get banned.