Tether loses money when buying USDT back, at whatever price. Sure, as long as they are buying it back at a smaller price than they originally sold it, they're still ok - but it's not in Tether's interest to give away its cash for USDT (since there are much better ways to make money off of cash than trading it for less than 1 cent). Especially since Tether can just print more USDT whenever they feel like it - it's not like they need to buy USDT before they can sell it again for 1$.