Why did the Supreme Court decide not to decide the same-sex marriage cases?

So, everyone's trying to figure out why the Supreme Court decided not to decide the same-sex marriage cases. I can't believe the reason is that the court didn't consider the issue very important because almost all lower federal courts have agreed on the issue. Of course it would be important for the Supreme Court to have the authoritative last word on the issue!

Amy Howe of SCOTUSblog says:

Strategy may have also played a role in the decision to deny review. The Court’s four more liberal Justices – Ginsburg, Breyer, Sotomayor, and Kagan – may have been content to leave well enough alone, from their perspective. Put another way, they may have preferred to let the tide of decisions striking down state bans continue to flow steadily, rather than risk a broader decision which might turn back that tide altogether.

OK, that's fairly clear. I'd also add Kennedy to that list.

But she finds it "harder to imagine ... why some of the Court’s more conservative Justices didn’t join forces to grant review":

Indeed, it was nearly impossible to fathom that they would allow the lower-court decisions striking down state bans on same-sex marriage to go into effect without a fight, even if (as the conventional wisdom has surmised) they remained concerned about their ability to persuade Justice Anthony Kennedy to join them in upholding the bans. But apparently they did, and we may never know the full story until a Justice’s private papers are released, many years from now.

Here's how I see it. The 4 conservatives should assume, based on what they know about their other 5 colleagues, that any Supreme Court decision on this issue would conclude that same-sex marriage is a constitutional right. And they might dislike that result, but they're smart enough to realize that's the only result that can possibly be supported by citations to Supreme Court case law. Or perhaps they basically think that'd be a fine result, but they're uncomfortable enough with it that they'd rather not be the ones to make the decision. Even if they're firmly convinced that the bans are constitutional, surely they realize that the most they could accomplish is a dissenting opinion with no legal effect; the only effect would be to tarnish their legacies and forever associate themselves with "the wrong side of history." In short, the conservatives had no good way to decide the case, so they decided they'd rather not decide it.

ADDED: One more possibility I left out: Perhaps the 4 conservatives have a strong desire for a ruling saying the bans are constitutional, so they want to do anything possible to increase the chances of that happening. And they think there's no chance with the court's current personnel, but there's some chance if at least one liberal or Kennedy is replaced by a Republican president. So they might not think they're very likely to win, but they at least want to give it a chance, and they've figured out that their chances are better if they wait.