Why not short leveraged ETF’s? What am I missing?

Why not short leveraged ETF's? What am I missing? UVXY is one example. It decays anywhere from 25%-50% per year. If you short it by borrowing shares it is very unlikely you can loose. Even if it goes up it will decay back down – always. Assuming you can find shares to borrow and at no interest or very low interest (2% a year) how can you loose long term?