Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Actually, the reason people do not change to it, is because The Gimp is not really a professional tool as it is limited in so many ways. Such as the fact that many photographers use LR + Bridge as a major part of their PS workflow, so using Gimp would be adding many, many unnecesary hours of work to their day, then there's the crippling lack of CMYK support.
there's a cymk addon of some sort (google finds it) I've no idea if it's good (enough), since i find photo-editing (beyond a little cropping) a waste of time (sorry, just being honest).
The Gimp is certainly capable of producing good work, but it's simply a copy
imitation (though in some ways not)
of PS which is running several iterations behind the real thing. The later versions of PS are much better, much more powerful and save more time than earlier versions and why people tend to upgrade PS, despite the cost.
In my limited use, cs2 was significantly more useable than ps7 (which was nearly unusable). gimp circa 2004 was somewhat bettrer than ps7. None seem capable of what i wanted to do (cleanup line art while maintaining respect for, or just awareness of, pen lines).
Plus the time taken to learn this inferior product could be spent more profitably doing some work in PS, which will earn you money and pay for itself many times over, way before you get to grips with Gimp. So the 'free' aspect doesn't actually pan out for professionals as time is money, so Gimp will prove quite expensive in fact.
Gimp's biggest obstacle is that PS is the neomonopoly in commerce. There's been a similar problem with 2d cad since the mid 90's (if not earlier) (and you know which cad app is the 9Gigagram gorilla...)
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.