Orcs that have nothing to do with Tolkien's orcs.
I seem to remember these guys being industrialized, miltaristic, and created from tortured elves or mud. Apparently they were based on the Germans from WWI or something.
Why do people turn them into noble savage Klingons/Native Americans/Africans?
1) Tolkien's orcs are irredeemable evil monsters. Baby orcs? Evil. You take an orc, give him a bath, take him into civilization, give him a job and a home - and he'll eat your face and play with your innards. So whenever you see orcs you slaughter them, no questions asked.
Some people do not like to play in a game with irredeemable evil and moral absolutism*. Evil humanoids are so due to nurture (culture, environment, personal choice, etc), not nature. But, orcs are still "The bad guy". Or at least, orcs are still "to be fought". In order for orcs to be fought, but not be Pure Evil, then they're given cultures that are warlike (Klingons, Apachi, etc), but are not evil and have depth.
This way, when the PCs kill all the orc warriors and find the women and children, they don't instantly slaughter every last one.
2) Some people like playing orcs. Half-Orcs were in the game in 1e, and in 3e, so they needed
something as far as a cultural heritage. An entire race of rape products is boring to some.
3) When you've been playing D&D for the last 20 years, fightin' the same old orcs gets boring. So, the same old orcs get a makeover.
4) Warhammer/Warcraft.
5) Got a better candidate for a Klingon/Noble Savage race, pre-4e?
*Moral absolutism and irredeemable evil in humanoids or more "natural" monsters. Everyone I've seen who doesn't like irredeemable races have nothing wrong with, say, demons/devils being always evil, or saying ghouls are evil, etc.