D&D has it roots in war gaming and I suspect that's a big reason why some races were just inherently evil. The creators weren't really trying to come up with a cohesive world they were just trying to come up with a reason why that elf, dwarf, and human were kicking down doors, killing a bunch of orcs & goblins, and taking the treasure. (Warhammer 40k is in the same boat. The setting was created as window dressing justifying why your Space Marines are beating the hell out of my Space Orks.)
And to complicate things, some of us see the use of inherently evil races in a game as a preference while others see it as a moral choice. Which leads to heated discussions because one side doesn't see what the big deal and gets upset when the other side fumes at what they see as very wrong. I find myself in the camp of the former rather than the latter. I can have just as much fun with a game where orcs are inherently evil as I can with a game where my character pursues relationships with them built on mutual respect and common good.