A cynical man might note that, if the director is a big name, then people will go see, and eventually buy copies of the theatrical release no matter what. Many of them will then turn around and buy the director's cut as well, once that's released at a future time. This being the case, why wouldn't the studios do this over and over, since they're benefiting? Especially since they usually screen different versions in advance - which should give them an idea whether there is likely to be a market for a different cut after the initial release or not...