DE stuff is part of the picture, but there’s churn outside of those too. glibc, which is used in practically everything, is the classic example but across the whole of the Linux desktop sphere, it’s unusual for libraries to maintain compatibility.

The only reason why Linux desktops work at all is thanks to package managers and their maintainers doing the heavy lifting of keeping applications and the libraries they use in lockstep. If it weren’t for that random programs would be breaking every other update.