I heard (so feel free to go down the rabbit hole and try to varify it, cause I am struggling to find a definitive source) that Blizzard was actually trying to make a 40k game but the deal fell through so they went for legally distinct lore. And one of the reasons all the cerabrates were killed between brood war and wings of liberty was because games workshop didn’t feel they were legally distinct enough and blizzard didn’t want to get in a protracted legal battle over them.