Shorting ETFs is expensive. You need to borrow the shares from someone in order to re-sell them, and you pay them for the privilege.

Futures work on margin with relatively low fees so if you wanted leveraged short exposure to the US market that's what you'd naturally trade.

One of the posters below who describes buying a put and selling a call at the same strike is describing a roundabout futures trade. The put/call method would have far higher transaction costs, though.