Startup: you look at something, plan, execute, learn skills as you go. Big company: here is x, do as I say. You must use these things from these teams, don't make it yourself.
Coping with the step down in responsibility is hard. Going from owning the entire stack to not even having a real decision in planning is very hard to deal with, especially if you've done that $thing before, and have to mount effectively an election campaign to change direction.
I think people with startup backgrounds in big tech tend to hustle harder in their careers than people that were “born” in that environment.
Being able to see, react and change based on changing business goals was the key to my career success. Being able to talk to decision makers and get something in place to mitigate risk/take advantage is a key thing in buisness.
Going from being able to do that, to not even knowing what the business goals are, much less getting access to any kind of decision maker is a tough change. Its like having the scope of a CTO and then going to a scope of an intern. You feel infantalised.
Or the startup was a stepping stone in your career. Big Tech wouldn't hire you, b/c you have a different background, so you work at a startup to develop experience and then switch to Big Tech.