I stayed a few years for a few reasons, first because it is still a good company with a “real” product, and also because 99% of my time there was spent working on open-source (clang/llvm).
When I decided to quit, it was in part because of their open source policy.
There are tons of developers who not only don't care about writing open source software on the side, actually go home after working 8 hours a days on computers and decide not to do any code at all and spend time on other hobbies, with their family, etc.