Open source, yes. Copyleft, no. GPLv3 forbids what many of these devices do. It is why GPLv3 is so feared by many companies, like Apple, why the GPL was gradually purged from macOS.
Painting it as some kind of irrational fear is misleading and counter-productive. It is perfectly logical for Apple to forbid GPLv3 code.
Quite frankly, GCC committed suicide by switching to the GPLv3. Both Apple and Google have entirely abandoned it. Apple invested tens of millions of dollars into building Clang as a direct result of the license change. And now even the BSDs and many embedded Linux platforms have switched to Clang, leaving desktop Linux and a few esoteric systems as the only remaining use cases for GCC. Yes, GCC is still around, but no serious company will invest in GCC for anything new ever again.