Why should they apologize? Everything they say is true.
GNU software absolutely has been stagnating for the past 2 decades under Stallman's leadership. It is a little known fact that in 2005, there was an offer to merge the LLVM project into GCC, and assign the entire copyright to GNU. The patches to do so were even submitted. [0]
They were rejected [1], because GNU wasn't interested in producing a modular compiler. They thought that if the compiler was allowed to be modular, then it might be used by proprietary software behind their backs.
But it turns out that modular compilers are generally quite useful, even for huge quantities of FOSS software. So the LLVM project continues, outside of GNU, and here we are 15 years later and essentially all academic research, and all new tooling development, happens in the LLVM ecosystem. Massive self-inflicted wound.
And yet, the stonewalling [2] and bridge-burning [3] [4] continued, long past the point of rationality. Continuing to object to development of useful tools even after the damage was done. At this point, just pissing off a lot of people who were interested in doing the work to help improve the usefulness of GCC.
And not limited to this topic, either. Such as when Stallman decided to leverage his "veto power" in opposition to removing an abortion joke from the glibc manual, against the consensus of nearly all of the glibc core team, despite not having contributed to glibc himself in years. [5]
And if I was interested in continuing to dig through mailing list archives, I could probably pull out a bunch more examples.
[0] https://www.phoronix.com/scan.php?page=news_item&px=MTU4MzE
[1] https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00...
[2] https://lists.gnu.org/archive/html/emacs-devel/2015-01/msg00...
[3] https://lists.gnu.org/archive/html/emacs-devel/2015-01/msg00...
[4] https://lists.gnu.org/archive/html/emacs-devel/2015-01/msg00...
[5] https://lwn.net/Articles/753646/