It's the same as with Linux, GIMP, LibreOffice or OnlyOffice. Some people are so used to their routines that they expect everything to work the same and get easily pissed when not.
To think that gimp was build to be a tool analogous to Photoshop (PS) is naive. It was born to demonstrate GTK GUI widgets and to check boxes on feature list
GTK literally means "gimp tool-kit" GTK exists because of gimp and not the other way around. Also. Take a look at what Photoshop looked like in 1996 (around Gimp initial release), and tell me that's nothing like the gimp. They used to be pretty similar, but their evolutions diverged. Gimp just choosed to stick with the familiar interface, even in the light of PS' changes. Also PS had tens of millions invested in developing it. Had gimp got a tenth of those resources things would be pretty different for both projects.