It's the default on Ubuntu, Debian, CentOS, Fedora, and RHEL to name a few.
QT has an history of being connected with non-free SW licenses, therefore commercial (or company sponsored) for those distros to rely and invest on such project is risky.
However, why argue if we can check the actual stats? [1] GNOME seems to be well ahead for now for desktop GNU/Linux. But the dip in the February, when the Steam Deck was released, is interesting.
Because nobody has actual stats. Your link is from one attempt to find some stats, but unless every major distro activates it by default (which they will probably never do on account of privacy issues), it's a tiny and biased sample.