Fedora may be becoming the default for desktops, not for servers (Debian possibly the default for servers).
Why do you think Debian for servers only ? Did you use Debian SID or Testing as a desktop ?
Fedora is upstream for RHEL, which is absolutely dominant in the server space some sectors that require enterprise support.
Actually on servers RHEL is still the default (43% server OS market share), followed by Ubuntu at 34%, Debian at 16% and SuSE at 11%.
https://commandlinux.com/statistics/linux-server-market-shar...