My reasoning can be found in the open letter posted on the GNOME Foundation mailing list here: https://mail.gnome.org/archives/foundation-list/2019-October/msg00001.html. A web copy can be found here: https://telegra.ph/Open-Letter-to-the-IT-community-the-GNOME-Foundation-and-Niel-McGovern-10-02.

[The GNOME Foundation deleted the thread but I have archived it here: https://notabug.org/JakeDP/free_raven/src/master/files/Open_Letter_to_foundation-list_GNOME_archive.tar.gz. There is also an alternative Free Software friendly site to view the open letter: https://notabug.org/JakeDP/free_raven/wiki/Open+Letter+to+the+IT+community%2C+the+GNOME+Foundation%2C+and+Niel+McGovern  -Jake D. Parsons edited September 03, 2019.]

In short Neil McGovern overstepped his office by using it for libel against Dr.Stallman (RMS) and then used social pressure to blackmail him and the FSF in a personal blog post here: https://blog.halon.org.uk/2019/09/gnome-foundation-relationship-gnu-fsf/.

The attack on RMS is an attack on free software and while the GNOME Foundation use the GPL and GNU software the use of false accusations of a horrendous nature is unethical and unprofessional coming from the Executive Director using his professional position for libel and politics. The resignation of Dr.Stallman is a step backwards for the Free Software movement. The GNOME Foundation is a major user and distributor of Free Software and we hope it will take responsibility for the anti-free software activities of Neil McGovern using his office to do so. Responsibility to Free Software as a major distributor and user of Free Software we call for the GNOME Foundation to remove Neil McGovern from his position and any association. Or for Neil McGovern to take responsibility upon himself and resign himself.