GCC was also designed to make it very difficult to modularize on purpose, I believe, when copyleft was still in its infancy.

https://gcc.gnu.org/ml/gcc/2007-11/msg00460.html https://gcc.gnu.org/ml/gcc/2004-12/msg00888.html

In retrospect I agree more and more with stallman that perhaps we should be actively avoiding helping to build proprietary software, but the tactic they used failed badly, hurt the quality of the software, and turned away prospective contributors such as myself.