[kazinator]

Many proprietary programs also get used because they are good enough. Not everyone wants to do a simple thing using some UI that has grown into a Boeing 747 cockpit.

Some Windows users use neither GIMP nor Photoshop to crop an image, but rather MS Paint, which is comes with the OS, so it is "no additional cost", and requires next to no training to use.

MS Paint has vastly diminished functionality compared to either GIMP or Photoshop.

[magduf]

Maybe cropping wasn't the best example for me to use, but there are many people who want to do more advanced photo editing than that (which is beyond the capabilities of MS Paint), but do not want to pay $$$ for Photoshop. Those people frequently use GIMP, simply because it's free and it works well enough.