* Microsoft is supporting CLANG.
* Android switched from GCC default to CLANG default.
* The CLANG development community, combined with the LLVM development community, are both extremely robust.
* GCC used to have full time commercial developer contributors working for Google and Apple and other large companies; most such companies have migrated almost entirely to CLANG/LLVM support.
* Because of better management and the army of full time commercial developers contributing to it, CLANG is better in practically every conceivable way at this point than GCC. If GCC weren't GPL, CLANG would likely be (at most) a fork of GCC, and may have been merged back into trunk by now (this happened to GCC once before).
CLANG is also an excellent example of how a completely permissive license can be sufficient to encourage big companies to contribute their changes back to the commons. All of the GPL fearmongering would have you believe that CLANG couldn't exist, and yet it thrives.
And printer drivers are still almost all proprietary [1]. So GPL didn't even achieve the objective that inspired it.
GPL did prove that open source CAN work, and it jumpstarted the open source movement. But its time has past; enough people understand the benefits of contributing to open source that the coercion is no longer necessary, and in fact is harmful.
[1] Some printer drivers have been reverse-engineered for Linux, certainly. But modern printers frequently leave so much processing for the host that their drivers are nontrivial, and even when there exists "free" drivers for Linux, they pale in comparison feature-wise to the proprietary drivers. I'm sure there are exceptions.