Don't think it has anything to do with the size of the gay population, but more that for the past several months at least 50% of the populace has shown support for gay marriage rights.
Personally, because individual State's are attempting to force the definition of marriage into biblical standards, marriage no longer has a place in State/Federal Governments. The US should stop recognizing it in the tax code and every other entitlement it receives, and only recognize Civil Union.
I wish the conservatives would get over this, but I really don't think they will. And unfortunately, that means it violates the Constitutional 'wall' between Religion and State, and therefore is illegal in the US.
I'm honestly shocked no one has sued the Government yet, because any lawyer worth a spit could win that one.