Technology

Because Linux distributions can be created free-willy. Just check out Linux From Scratch, Gentoo, etc. Same with live boot from USB, same with stripped down server distros like Alpine — you have the same issue.

I don't want to be "that person", but here's how it could play out...

The "free-willy" distros would not fulfill the "trust" requirements needed to pass the "certification process". You can still use them, but think of it like running custom firmware on your cellphone: you're not going to be able to access your bank, but somethings will still work.

Larger distros (Red Hat, Ubuntu, etc) would pay to pass the "certification process", but this would come by making certain concessions:

1. The kernel would not be allowed to be tainted. Which means you can only use official kernel modules provided by your vendor (no self-compiling)
2. Certain kernel modules would needed to be removed (or nerfed). For example the Fuse filesystem.
3. You could probably keep root access or at least a nerfed version of it.

Then with theses concessions, your PC world be deemed "reliable" to perform the necessary age verification and have this confirmation passed through your browser to your favor porn site.