[Gualdrapo]

That's exactly the problem.

Not only that they use privative products - it's that people think about Krita as an alternative to Photoshop, as Krita is intended for digital painting rather than general raster image manipulation. Hence narrowing the target of Krita to a much smaller audience.

[fluoridation]

To an extent, it is, since a lot of artists use PS to draw/paint. For those people, Krita is indeed an alternative to PS.