Maybe I'm dense but I don't get the 'driving away' bit. Not doing something is the right of any creator. Stallman is the guy that first of all wrote the software and made it possible to fork. So if the functionality is really that much in demand get it over with and fork it so you can correct all these perceived slights and the world will be a better place for it.
But don't try to pressure the man into doing something he clearly does not want, whatever his reasons, that's akin to complaining the gift you got wasn't quite what you wanted.
I don't think anybody does care, they just like to argue with Stallman. Clang's parse trees are cleaner and more useful than GCC's ASTs. Even if this were implemented in GCC it would be limited and inferior, so why bother?
But don't try to pressure the man into doing something he clearly does not want, whatever his reasons, that's akin to complaining the gift you got wasn't quite what you wanted.