Lots of people in this thread missing that unsweetened yogurt options are probably not distributed evenly across US supermarkets.
Your local coastal city store might have a half dozen plain greek yogurts but I bet there are plenty of areas where they are not stocked because they know it won't sell.
You would lose that bet. I eat plain unsweetened yogurt. I have seen it on the shelf in supermarkets everywhere, not just coastal cities.
But hey, don't take my word for it. Most large supermarkets now offer online ordering. Pick a few small Midwestern cities at random and look what dairy products the major local supermarkets have in stock. It's hilarious how people keep posting uninformed comments here without taking 5 minutes to do some trivial fact checking.
Your local coastal city store might have a half dozen plain greek yogurts but I bet there are plenty of areas where they are not stocked because they know it won't sell.