Gimp is one of the few FOSS projects with some notoriety outside of tech circles. It, VLC and Linux are possibly the only names I could expect some random person to have heard of. Changing its name would probably torpedo years of work to become seen as a reliable piece of software and send it back to the realm of "software that only people who watch the code repository know about".
And the whole changing the name to avoid offending someone is a losing battle in the first place. According to this thread, "rice" is potentially racist. I had no idea anyone could find "Gimp" offensive, but apparently they can. By this point, it's part of american internet culture to be offended and no word is safe from americans turning it into a slur, dog-whistle, etc etc and advocating that everyone else in the world should stop using it.