It’s getting harder and harder for kexts. You can’t readily compile those from source and install them yourself without a developer license , anymore.

You currently technically still can, I believe (restart in some safe mode and disable a protection mechanism of sorts, iirc), but the trend is not towards openness. Honestly I don’t doubt for a second they’re doing it purely for the sake of security, but that doesn’t really matter for the GPL as far as I’m aware ?