> that multi-million and even billion dollar tech companies don’t have perfect websites in terms of UX

I would have thought it'd be the opposite.

It implies have hundreds of teams and UI / UX often is "scaled" in weird ways where everyone does their own thing and becomes a giant mess.

Everything is "correct" when you slice it enough. So from team A's perspective this might be a gain. When you are a part of a team you only see and own this part. That's your KPI.

Unless there's real and working governance (often very very hard) then it's not happening. To get that governance you need company direction and company buy-in that stops managers trying to push new features fast to infinity.