I hope Gimp will switch to GTK3 at last. It's one of those projects that's still stuck with GTK2. Or even better - Qt ;)
No, the problem was with Qt itself. The whole reason GTK was created, is because Qt wasn't really FOSS. Only much later Qt was really opened up. So yeah, today Qt is open and it's clearly much better. But the damage was already done, and the split happened.
I think the grandparent is definitely right. A lot of projects were started post-1999, when Qt was already open. But GNOME was the default desktop of many distributions (including Red Hat and later Ubuntu). Moreover, it is harder to bind Qt in order languages, since it is C++. There was a strong dislike for C++ in parts of the FLOSS community.
"You should completely rewrite this project, consisting of hundreds of thousands of lines of code that people have worked on for years, using the tools I like better!"
Because that's pure gold.
For extra enjoyment, look at the way they convert a function definition to Rust. You'd hope that the new version would be at least somewhat nicer than the original, but of course not. As lng as it's Rust it must be better, right?