The "stable" part in the name suggests that it does in fact offer a return as a defensive investment against the volatility inherent in other crypto assets.

If Bitcoin is going down, you sell and buy USDT instead, then two months later you trade the USDT for 20% more Bitcoin than what you started with... Measured in Bitcoin, you got a 20% return, and it was made possible by the asset-backed security in which you invested in the meantime.

Regular money market funds didn't pay anything when interest rates were negative. They are still securities.