It's the other way around. The widget library was built for Gimp, then took a life of its own. Note that Gimp still has not released a version ported to GTK 3 (but the port is done since last year, in the 3.0 branch), released 13 years ago. GTK 4 has been released 4 years ago.

If you're doing digital painting, it's probably just what you're used to.

I disliked Krita until I spent a few weeks learning it. Once I found the "Krita way" of doing things, it was actually a much better experience than Photoshop offered for digital painting.

I'd recommend finding a YouTube video where an artist takes you through how they use Krita to see some of the workflow and most common shortcuts.