You have to borrow it to short it, so there's a 1-3% APY cost associated with shorting it. You have to calculate the tradeoff of the likelihood of it going to 0 within the next couple of years vs the cost of borrowing USDT to short it.

Say you short 1M$ worth of Tether, it goes belly up within 4 years, it cost you like ~40k$ to short it, but your upside is 1M$. If it never actually fails because the market is irrational or by some miracle Tether was doing the right thing, then your cost depends on when you close your position. It's a relatively cheap way of making lots of money depending on your conviction on Tether's likelihood to fail.