we (sort of) did though!

cows/cattle are basically just walking slabs of muscle, which is GREAT for eating them, but not great for riding them because it makes them very slow animals. but what cows ARE great at, turns out, is pulling things!

cows/cattle have been used to pull really heavy stuff since basically the Paleolithic, playing the part of the bulldozer to the horse’s 2003 Toyota Corolla across the centuries.

need to go to the next town over in a reasonable timeframe? ride a horse. need to relocate your entire household, furnishings included? HOOK UP THE OXEN, PA.

(yeah, “oxen” is just the word we use for cattle when they’re being used as draft animals, but they’re still just cattle. surprise?)

and as for deer, deer generally suck as mounts in all possible ways compared to horses, with their skittish nature, smaller size, and lower endurance! but some larger deer HAVE found work, again, as a combination of general draft animal and walking food storage. the Sami peoples of northern Europe and the Nenets of Arctic Russia in particular keep strains of semi-domesticated reindeer for transportation and food.

but in areas that DON’T require a super-hardy native breed of livestock to tolerate extreme weather conditions, people have pretty much stuck the standard “the horse bears the rider, while the ox pulls the plow” model.