The problem that's being solved is that vendors are incompatible, which could easily be solved if they were compatible. They all run a linux kernel. They all use ELF and x11 and opengl. If I compile 'hello, world' on one distro, I can drop it onto another random distro and it'll still work, but after a certain threshold of complexity, that stops working. It doesn't have to stop working.

Even a simple hello-world doesn't work across distros since it requires a specific version of glibc.

The glibc version tagging has to do with specific symbols; hello world just uses printf which is there since forever. (Actually the compiler probably optimizes it down to a syscall but.)