To be fair, this is because they are, ironically, professional image editors.
GIMP has historically very bad GUI. This is common in open-source projects, where technical people develop the software based on the capabilities. There is rarely UI/UX designer in the project that makes sure that average Joe can do the thing as well. So, technical people likely would disagree with these professional image editors, and they could demonstrate the same end-results with GIMP as these professionals do with other software. Professionals just had no idea how to.
I have no idea where you got this info from but it is 100% wrong. Of course GIMP can be used for commercial purposes. Or any purposes you want, really. The GNU GPL does not prevent commercial use.
see also https://www.gimp.org/docs/userfaq.html#can-i-use-gimp-commer...
The original meaning is a slur for someone mentally or physically disabled.
The subsequent, sexualized meanings were derived from that.
Pretty much one of the worst things I can imagine, and certainly the worst product name I've ever heard, by far.
And to think they picked it on purpose!