Its somewhat substantiated by the fact that getting into modern big tech is pretty much focusing on the interview process, which has almost zero to do with actual real world development.

Furthermore, having worked in big tech, most of the roles that are getting filled are essentially "busy work" - i.e here is a entire proprietary build system, barebones service and deployment pipeline, all you have to do is add logic. Someone who has worked in this type of environment isn't going to succeed at a startup where you have to build systems from scratch.