Apple shies away from GPLv3 code. They ship a ton of GPLv2 code, though. And as you mentioned, even if they didn't, it just takes a moment to install Homebrew and get whatever else you want. Apple doesn't stop me from installing a new Emacs.
Sure, Apple won't stop you. But the defaults matter. If you're writing a shell script and you want it to run on MacOS, you need to target the ancient version it's actually shipping, or you have to tell your whole team to install a later version. If your servers are running Linux then you'll be dealing with platform inconsistencies all day long. Ask me how I know.
