Why didn't they add horses to New Vegas? For instance, say there was a quest to help a rancher with the end result being him granting you with the horse. In hardcoe mode the same rules would apply, you'd have to care for the horse too. I know Skyrim had them, not sure about Oblivion though. Any thoughts?

Horses died off during the great war.

Technically, everything should of died off. Im just saying, they made a pack brahmin. Why not a mutated horse?

Any number of reason from they simply didn't want one, to resource limitations, to they didn't want Fallout to be too like TEs, who knows.

I am surprised by the apparent lack of any other beast of burden outside of brahmin.

You'd at least think some crazy SoB, possibly in the BoS, would have tried domesticating and riding a radscorpion.