Why are cows and goats not kept in cages?

They're not kept in cages because they aren't suited to be kept in cages (quite frankly, no animal is meant to be kept in a cage, but that's a different matter to discuss in a separate question/discussion). They're big animals, unlike small ones like birds and defecate a lot (moreso cows than goats), but the biggest reason is their feet. They do not have paws or actual feet like chickens do where they can feel the bottom of the cage, they have hooves which are really easy to get trapped and stuck in the holes at the bottom of the cage, plus they cannot feel the bottom of the cage to keep in the cage. They don't like having their feet trapped and tend to panic (and as a result, injure themselves) when they get their feet stuck.

It's also really, really expensive to make, buy and maintain such cages for such large animals. It is said that veal calves are kept in cages, but really they're small elevated stalls where they're kept until its time to sell them to slaughter.