They are probably designed to be like that so you can rush into accepting the tracking across the web.
The web has become a sad place where most of the content is made for showing you ads and tracking you around, therefore tracking cookies are needed, therefore tracking cookie permission banners are displayed.
If you don't click accept on the very first page, websites can't connect you to where you're coming from, which is why they're like that.
I mean, in theory they could do that retroactively, but that would be waaay to complex.
Popular cookie banners enable services by executing their javascript. There's no event tracking mechanism whatsoever. Cringe fact about cookie banners.
It's probably because every engineer spends as little time as possible on it, since it's boring af. It's annoying & boring to implement, and once it's done, annoying to everyone that sees it.
The web has become a sad place where most of the content is made for showing you ads and tracking you around, therefore tracking cookies are needed, therefore tracking cookie permission banners are displayed.