I've seen video evidence of human-orc pairings on pornhub.
Frankly, they were kinda hawt.
Someone already mentioned medhiv and Garona, but I think she is a draenei/orc hybrid, dunno if that counts.
Are you counting only WoW? Some has mentioned Garona/Medivh connection.
Other fantasy universes has tons though. Half-Orcs are a crucial part of DnD for example.
Are there any tauren-anything pairings?
Society has this fad where inter-racial human relationships, as well as inter-species with things that don't look almost human, are frowned upon in the media. Give me one example of a mainstream show that shows an interracial couple.
Blizzard itself is very Disney-esque safe, so human-elf is as far as they're gonna take it. Yes, I know, Jaina. But Calecgos has a human form.