Why are there no open source standalone photo editor for Android?
There's a bunch of closed source ones, the best of which were brought by Adobe, but there's never really been a big open source effort.
GIMP say that the lack of separation between functionality and UI is why they're not behind an effort. That said they said they'd be happy to stick their name on an effort.
But this takes me back to my original question, why are there no open source photo editors, despite their popularity?
Likely because editing on desktop is much more common and so gets the majority of the focus. A comprehensive photo editor for a mobile platform is probably just too niche to attract enough developer interest
Unfortuantely, how I see it, FOSS devs are more likely to cater pro/enthusiast users who are more open to try and support desktop solutions. Meanwhile, indie Android devs are also likely to monetize their work. I can't blame them, though.
Krita is available, it may not be great yet as far as mobile friendliness in the interface, but I see they always do work a bit towards that in their release notes so hopefully it can grow to become the best one, it won't be as good as an actual photo editor maybe, but it'll be the closest we can get in the foreseeable future.
For simple edits there is still Simple Gallery Pro
On the flip side, I grew up most of my life only knowing gimp could stand for gnu image manipulation program, and is still the first place my mind goes to when I hear the word