Probably because GenX and Millenials (the actual people who created and played these games respectively) don't like being associated with the generation that's destroying our society and planet whilst being completely out of touch with reality. It was boomers who tried to ban these games, remember?
bUt BoOmEr iS jUsT sLaNg FoR oLd PeRsOn NoW
ok zoomer
A truly unique feature of the retro FPS genre.