Sheep are incredibly expensive to farm as well which is why the meat cost so much.

People think sheep are dumb but that isn't true, they are anti-intelligent, they secretly hide vast intelligences that they use to come up with ingenious ways to injure or kill themselves. You can put goats in a field and fence them off and be reasonably confident that you will still have all of your goats when you come back in the morning.
Sheep on the other hand will use their psychic abilities to manifest some broken glass, and then step on it.

Then the supermarkets don't want to pay very much for them and so now you've spent a lot of money looking after them and got very little in the way of return.

The only reason that sheep were traditionally found was because you could put them on pastures of land that was completely unsuitable for any other animal. But it's the supermarket aren't willing to pay a fair price then that doesn't really count for anything.