I suspect that GPL2 was instrumental in guaranteeing that the work sacrificed into the common pot of Linux kernel is not going to be taken by a competitor when it's still unpolished, closed, and used to achieve market domination.

FreeBSD came before Linux (as 386BSD), and is also active used by the industry. How much code did Sony or Raytheon shared back to FreeBSD? (LLVM is not FreeBSD proper.)