And why would they want that? Is there anybody who doesn't want clarity on the matter one way or the other? If they would have wanted to delay ruling on the constitutionality of inequality in marriage legislation for all of the US all they would have needed to do was, not take up the proposition 8 case at all and all that would have done was restoring marriage equality in California.

What they have on their hands now is, most likely, a very ideological fight within the court on whether or not they should give equal protection to gay people with the effect of granting everybody everywhere in the US the right to marry a person of the same sex. I have no doubt that the likes of Scalia will try to abuse the fact that marriage isn't in the Constitution (thus sidestepping the equality and necessity questions).

P.S. it's good to see that the term 'gay marriage' is one I see less and less.