The reason you've never encountered it outside of the image editing program is the same reason you don't encounter the n-word in public. It's prima facie offensive, so people don't use it unless they're trying to be assholes.

That's why to most people you end up looking like an asshole when you suggest they try GIMP. Then you have to apologize and agree that it's a terrible name, but a great image editing program. But the damage is already done.

It's as simple as that, just like as if it were named after the n-word. What else would you expect?

The g-word is arguably just as bad as the n-word, and it's not the sexual connotation, it's the fact that it viciously punches down making fun of disabled people.

And people who act that way and use those words on purpose are assholes.

Donald Trump mocks a reporter's disability:

https://www.youtube.com/watch?v=mdLfkhxIH5Q