Unfortunately - the OSS world has a shortage of good UX people, and the engineers tend to be the ones steering the ship.
I would point to Eclipse as another classic example of "obviously designed by an engineer". There's tons of functionality under the hood and it's a fantastic jumping-off point for further customization... but its layout is intensely non-intuitive in so many ways compared to a purpose-built IDE.
Everything is locked away in menus and "perspectives". If you're writing a Java web app - do you want the Java perspective, the Java EE perspective, the Web perspective, or the Debug perspective?
I hear GIMP's no picnic to work with either but can't confirm personally.
I fear the day "good UX people" come to GIMP and Blender.
It used to be that OSS was developed by people that actually used it. Maybe it wasn't pretty, it had a steep learning curve, but it got things done and was efficient once you learned how. Often you got fresh perspectives on how an interface could be done, since people got fed up with existing solutions.
Nowadays you get UX experts preaching how an interface is supposed to look like, which mostly means copying Apple or Google. You get tons shiny whitespace. Burger menus, because that's what "everybody is used to".
GIMP with "good UX people" would turn into a bad copy of Photoshop.
GIMP is pretty easy to pick up if you've used desktop apps before. It follows the sort of conventions you'd expect.. Blender, on the other hand, has a very unique approach to UX.
cough Blender ...