Not true, I am a naturalized US citizen, and don’t have a middle name - it was never an issue and I was never asked to come up with one. My son was born in the US and also doesn’t have a middle name.

I think “popular” is stretching it here, Debian GNU/kFreeBSD is dead now, and while Hurd is interesting, it has ways to go.

Alpine is actually popular, particularly as a lightweight host OS to run docker.

You can have a Linux distro without GNU -Alpine Linux is a popular example