Having worked at a few, I can confidently say that the environment is just not conducive for good design thinking, solid polished execution and close collaboration with PMs and Engineering. Active participation outside of your scope is discouraged, filing bugs and getting them fixed is hard, rapid experimentation is met with so much friction and the average day is filled with so many meetings and catchups that you're left with no creative energy to think deeply about anything.
The secret to great design is... (hiring great designers)