Deer is simply harder to farm, cattle are more domesticated (docile).
In NZ we do have deer farms, and we can buy venison in the supermarket. Though it's generally red deer. Most of our venison gets exported though.
Fallow Deer meat is the best meat I've ever tasted, it's sweetish, very light and tender, and has no fat. It makes even the best beef look like 3 week old roadkill. But it's very difficult to farm, and a smallish animal compared to red deer. Occasionally I get to hunt a couple of area's that carry fallow, last time I brought back 3 beasties.
Here's one about to get chopped up with my hungry little carnivores waiting:
Believe it or not my wife does all the butchering, we get every little piece as we have a mincer. Of the last 3 I brought back we got around 16kg's of prime venison mince from offcuts which made delicious burger patties.
In NZ deer is considered a pest (introduced species), hunting is all year around and free
While we're talking meat, we also eat hare meat (aka Jack Rabbit in the USA), rabbit, and feral goat (the young nannies). All are excellent and healthy meats commonly overlooked. I took my eldest (nearly 7 now) hunting and shot a hare just last night.
One of these guys...
They have very long back steaks which are great for frying, and lots of meat on the hind legs. Once again the meat is a lean red meat, and the female of the species tastes best
. Sometimes I'll roast them - rest of the time they go into the mincer (great for pasta's). A typical hare will give around 2.5pounds of healthy lean mince.