I can't understand the logic for this

(1) The last major user-interface change for users in Gnome occurred with 3.0. That change was controversial, for sure. But Gnome 3 was released in 2011–13 years ago. So, from a user’s perspective, Gnome is not making major interface changes all that often. Mate and Cinnamon originate from the old change.

(2) Also controversial and more frequent are the changes to the JavaScript code that runs Gnome shell and can affect extensions. Changing the base code happens; this is not unusual or “arbitrary,” necessarily. The choice was to allow extensions full power to change the desktop in all sorts of ways, but any changes to the base code can affect the extensions, which are essentially hot patches. The alternative was to present API stable extension libraries to allow extension authors to change the desktop in more future-proof, but limited, ways. My understanding is that the community, including the extension authors, greatly preferred the first approach—which is what Gnome does. The downside , of course, is that extensions might break from release to release. The Gnome folks try to mitigate this problem by releasing an extension-port guide with new releases.

So, I would dispute that Gnome has a history of making frequent “arbitrary changes.” That said, System76 is free to go its own way and reinvent the desktop in a way that is under the company’s control. The upside is that the company is not beholden to the Gnome community or legacy code—it’s a fresh start. The downside is that starting mostly from scratch is very difficult. If System76 can pull it off, kudos to it.