You've already responded to my 'how so'. I would've said 'more users' you've said 'crap users.' Fair enough.
It's just that photo editing software has a relatively high learning curve. I think (anecdotal, I have no references for this) that due to the cost of photoshop many users start experimenting on pirated copies. Mostly kids & hobbyists. Years later they may buy a copy or take it with them to the workplace. By that stage, they're used to photoshop to the extent that it's the only option.
There's certainly validity to the theory that piracy helps protect market leaders. It's the reason Microsoft doesn't aggressively fight piracy in developing markets (and if they do address piracy, it is by making the software available for practically free through legitimate channels).
I'm sure there are some Open Source developers out there who do want every possible user, and want, more than anything, to oust their leading proprietary competitor. I'm only among them when I'm thinking like a business man, and trying to figure out how to make money from my software.
I think there might be more to it then that. I'm not really a user of image editing software (Seashore covers most of my needs) so I can't really say this for sure. But I get the impression that GIMP want to do things their way, not the photoshop way. Getting young users using GIMP first gives them a chance to do that.
It's just that photo editing software has a relatively high learning curve. I think (anecdotal, I have no references for this) that due to the cost of photoshop many users start experimenting on pirated copies. Mostly kids & hobbyists. Years later they may buy a copy or take it with them to the workplace. By that stage, they're used to photoshop to the extent that it's the only option.