But in our actual world, it's also legal but publishers may play dirty and somehow claim rights because you published something based on their edition?
Just thinking out loud.
maybe not totally, but mostly. Beyond that he does not care about it and isn't interested in it.
I code in C regularly, yet I do not care and am not interested in C after C90. Only some library features of C99 and that's about it.
Stallman's concepts of what is Lisp, how to use Lisp, how to implement Lisp, were formed long before Common Lisp.
If you're in that position, it's easy to have allergic reactions to requirements you don't agree with.
Maclisp and its successor Lisp Machine Lisp, were probably his biggest influences. Emacs Lisp is based on Maclisp - without the features of Lisp Machine Lisp like keyword arguments, Flavors as the object-system, ...