GTK is the Gimp Tool Kit. I expect GIMP to use the defaults: historically they created to toolkit for their needs, and so they should choose the right defaults for them.

Note that the above is historical. GNOME selected GTK long ago and has somewhat strong armed GTK development away from GNOME. I don't follow either project closely enough to suggest how much.

Here's an example that was just pointed out to me by prokoudine:

https://git.gnome.org/browse/gimp/commit/?id=52ad5bb2a11e39f...

The default situation was that the toolbox grabbed the focus when clicked. That meant various actions, eg. "Show/hide docks", didn't work if the last thing you clicked was the toolbox. That's an annoyance created by "accepting the defaults", that's thankfully now been fixed in light of real-world usability issues.

It's like they've confused the valid idea of an open source programmer being tainted by looking proprietary source code, with the ridiculous idea that a user interface designer would be tainted by looking at or using a proprietary user interface.

Some aspects of Photoshop's user interface are patented, but it's much safer and wiser to LOOK at them and be aware of them and read the patents, so you're consciously aware of what not to do accidentally, and able to work around them.

> I think they're generally just the obvious GTK+ default options, implemented without much testing or tweaking.

GTK+ is the GIMP ToolKit; the entire toolkit is GIMP's innovation.