That assumes there's storage space and that the June contract will stay above zero by June. There's no guarantee for that.Hence, there's a killer arbitrage opportunity if you can store the oil by buying the May and selling June.
That't the whole point. If there were storage, we wouldn't be seeing this anomaly in the first place.That assumes there storage space and that the June contract will stay above zero by June. There's no guarantee for that.

Lottery time one minute ahead, place your bets!
Brain teaser: Just how the f*ck can you settle a negative price? Am I being paid by the broker now that I'm holding at -35?