The Fedora leadership is elected the the community. Also most the community does not want to deal with KDE. KDE is great for power users and people who like customization. Outside of that most people want stability and simplicity both of which KDE is not.
The other issue is the installer and the enterprise. If Fedora switched to KDE by default then the downstream distros would need to as well as Fedora is the testing ground for RHEL, Rocky and Alma. I can’t imagine anyone wanting to run KDE on a server or corporate workstation.