I will only lose my time answering this one... since I am feed up with blizzard whiteknights.
Did you ever played Warhammer tabletop? Or read any Warhammer novel? Did you knew that Warcraft I & Warcraft II orcs and humans is a spin off from the same races that exist in Warhammer (WAAAAGGHHH became Horde, Chaos became Burning legion). The "Warcraft universe" you know, came from the changes introduced with Warcraft III (not to mention the huge renaming of units that came with TFT).
Why did you think Warcraft III is so important for Blizzard? Why they don't made a "reforged" Warcraft and Warcraft II? Why da frak you think Blizzard moves earth and heaven to retcon Warcraft Lore to erase what happened on both games? Did you ever know that when they were planning Warcraft I they tried to license Warhammer?
https://www.codeofhonor.com/blog/the...arcraft-part-1
Starcraft is a spin off from Warhammer 40k, this is OBVIOUS and there is nothing wrong with it (Warhammer 40k is a huge spin off from Starship troopers).
Protoss = Eldar - old race, bound by religion, webway users
Zerg = Tyranids - power of numbers, hiveminds chitin/insectoid like beings...
Terrans = Empire of Man, holy site of Terra, Space marines...
And to be honest had they stayed with the "grim dark theme", Starcraft 2 wouldn't had the mediocre lore it had.
So, Diablo is the only IP that blizzard created from scratch, without largely "borrowing" stuff from other IPs. But guess what? Diablo wasn't made by the Warcraft/Starcraft folks (Blizzard "South"), it was made by Blizzard North - which is long gone and took with it the "Diablo magic".