> I used Photoshop for 8 years, including for web development, before switching to Gimp.
> Gimp is good enough for everything one needs in web dev, is free, and has a vital feature Photoshop lacks: the ability to run on a Linux workstation. When developing software intended for Linux servers the value of having a Linux workstation to easily do local development cannot be understated.
Precisely. You're a dev for whom GIMP is "good enough". If you were dissatisfied you might make a new tool, but since GIMP suffices, you happily use it and see no reason for anything else.
Meanwhile, artists and designers who work in Photoshop day in and day out - the people comprising the bulk of Photoshop's actual market - overwhelmingly reject GIMP, and they don't generally have the capability to make a new tool, so they stick with Adobe.
At the risk of making an imperfect analogy, imagine you wrote a French textbook. French teachers overwhelmingly rejected your textbook and didn't use it in their classrooms. But at the same time, other language professionals sometimes found it helpful for small things like double checking the conjugation of some obscure verb, and they'd defend it because they found it useful. Is your French textbook a success? I'd say no. I'd say you're not only failing your primary market, but you're lulling fellow professionals into a false sense that there's sufficient tools out there for that market, which is doubly harmful.