Firstly, it's quite normal in a bear market. Bitmex is by far the biggest platform, where you can play shorts.
On the other hand, personally i'm looking for some licensed exchange.
Not so long ago, i found out about Covesting, which has the most valid license - DLT from Gibraltar.
If i'm correct, they will try to allow margin trading (like bitmex) in the future, but now i'm more excited about copy-trading, where you can copy some licensed traders.