The root of orcs as we think of them is Lord of the Rings, where they’re corrupted elves (or something like that). Literarily, they represent the evils of war. Tolkien orcs are evil.
Orcs have seen the furthest drift from those roots of anything from LotR. Dwarves, elves, orcs, and halflings saw some drift to generalize them for other tabletop settings. But the traits settled on for orcs in the 90s and 00s (strong, nomadic, clan society, warlike, brutal, noble savage stuff) can now feel insulting, because those traits are so often used in racist contexts, so orcs have seen a second drift away from those, too.
I don’t see much of a point to orcs anymore and don’t use them. Regarding 5e, I haven’t read its finished modern take on orcs but if I want Fantasy Mexico I’m just going to use human Fantasy Mexico.
I do disagree that fantasy villains need motivations beyond existing. Conscience and free will are required for protagonists, optional for antagonists. Illithids, vampires, and early Pathfinder goblins come to mind from fantasy. Strahd’s reason for being a villain is that he’s mopey. Everything in Cthulhu, likewise, lacks comprehensible motivation.
It’s hard to make an inherently evil villain that is a foil to the PC, but not every villain needs to be a foil. As a GM it can be really fun to wallow in a villain being unrepentantly, unthinkingly horrible.