Maybe because the parent has benefited from Paint.NET and it is logical to support them?
Because the parent apparently doesn't like those as much as Gimp / Krita etc? Open source is a noble goal, but not equal to worth donations / money.
Or the parent doesn't know open-source alternatives exist. It doesn't hurt to remind about them, seeing as their development would benefit more people in the long run.
I would donate to GIMP if they started caring about UI.
People who start with GIMP prefer its UI over Photoshop's. It's a matter of getting used to it, really. Or, failing that, "donate" to Adobe to get your ideal UI.