From Fedora Project Wiki
Because that comes with some types of disruptive changes which we do not perform in releases and which I do not advocate performing in releases. Rolling releases like Rawhide, Debian unstable, Gentoo etc. have no set points to do disruptive changes. So e.g. you wake up in the morning and your system no longer boots because your kernel upgrade from yesterday enabled libata and you had hd* hardcoded in some place. (Yes, I know that particular change is now a done deal, but there will definitely be similar changes in the future.) As I have explained several times, AIUI, a stable release MUST NOT get upgrades which "break things", e.g.: * require manual adjustment to config files, databases etc., * break support for existing user data (documents, configuration, savegames etc.), * knowingly introduce regressions, * remove features, * radically change the UI (but I don't think minor changes like a menu entry moving to a different place are a serious issue), * bump the soname of a core library on which dozens of packages depend (but I don't personally see a grouped update with a soname change and a rebuild of ALL packages using that library as a problem as long as it's only for a few packages), * change the API of a library in a way that existing applications using it fail to rebuild and cannot easily be fixed (in fact soname bumps MUST be accompanied by rebuilds of everything affected) etc. (and I think we all agree there. But that's why Rawhide is not the answer!), but IMHO (and there opinions differ), it SHOULD get upgrades which: * fix bugs, even if they're not critical or security, * introduce features in a non-disruptive, backwards-compatible way (e.g. there's now a new menu entry which does something cool, at worst that new menu entry might not work perfectly, but it shouldn't affect anything else).