I think, because of Fedoras atomic desktops. I didn’t use any of them yet, but it seems like Flatpaks should be used there, since one should (or can?) not install tradional packages there. Therefore Fedora provides the flatpaks anyway and they can be used on the non atomic desktops as well.
Another reason is, that you might not be able to install the latest version of an application as rpm package if a required dependency in the repo is outdated. A Flatpak usually does not have the issue since a newer version would include the fitting runtime. This said, I do think its not this big of an issue for fedora which is usually quite up to date. But if you run a distribution with LTS releases or something like Debian you will much more likely have older dependencies in your repositiry.
I think Gnome is the most beautyful Desktop out there. But it’s UX drives me crazy. I tried it a few times but never could get used to it. I always needed extensions to customize it to my needs. But that’s also what I want to avoid because extensions might break in the future. Therefore, Gnome is simply not the right Desktop for me.
But I’m happy for everyone who likes to use Gnome. The great thing about Linux: We have a choice!