Because largely-symbolic political gestures that effectively do little more than kick the can down the road to the point where it'll ultimately be settled by the courts which as going to happen anyway ain't just for Republicans anymore, the Obama Administration announces that it will no longer defend the asinine "Defense of Marriage Act" in federal court. Furthermore, they've publically declared intent for this to be a lead-in to an eventual repeal of the act. Translation: "Gay Rights supporters? Get out and vote for our guys next time - we need a majority to make this happen."
"DOMA" was essentially a packet of provisions that prevented any laws, particularly those concerning partner-benefits, from "blurring" the line between same-sex couples and married heterosexual couples; so all this really means is that the lawsuits against discriminatory practices in this particular realm can now be made without the innevitable prospect of "DOMA" being used to block it from going through. So... not really a sea-change, but a win is a win.
We now return to our regularly scheduled program of Republicans and Democrats both pretending A.) to be shocked - shocked! - that the other side is dealing with social issues before "creating jobs;" and B.) to believe that they can actually do anything about "creating jobs" in the first place.