>why not call it Gnome "Imp"
Because it's not an imp.
Because it's wholly unrelated to the Gnome project.
In fact it predates GNOME by three or four years.
It's the GNU Image Manipulation Program, though most people find that to be too much of a mouthful; hence "GIMP".
Yes, sorry GNU, brain-fart.
How is Gimp less of a mouthful than Imp; would it not be worth the change.
I've used it for about 20 years, have tried to recommend it to people and always feel embarrassed to do so: similar to if they called it "shit-head". Not so bad as if you were recommending someone try Brainfuck.
The GIMP sucks for discoverability IMO, but I too find it comfortable because I'm familiar with it; and have found other apps crazy hard to pick up (Photoshop some years ago; Corel Draw clicked fine for me though).
I think graphics can be a bit of a grab-bag to some extent so logically connecting methods to put then in a menu hierarchy can be tricky.