Some church leaders disappointed they can't whip people into hateful mobs

Too bad, guys.

Still, the opponents of gay marriage say they are puzzling over why such a volatile cultural issue is not spurring more rank-and-file conservative Christians to rise up in support of the amendment. They are especially frustrated, they say, because opinion polls show that a large majority of voters oppose gay marriage.

I think there's several reasons that it's hard to get people to care. As Prometheus 6 points out, people are just more worried about more pressing things right now. Though I would caution strongly against over-rating that as a reason. People were all too happy to direct tons of hatred at blacks when they had pressing concerns like economic depression and war that should have distracted their attention.
I think there's a number of social reasons. For one thing, I think alot of people, including religious conservatives, realize that getting whipped into a hateful froth about gays is causing people to question your sexuality more, because otherwise why do you care what others do? And of course, there's old-fashioned American mind-you-own-businessism, which doesn't help against temper racism or sexism but surely tempers homophobia. Then there's common sense, the kind that makes you realize what your neighbors do doesn't, or at least shouldn't affect your own marriage:

The amendment's backers contend that the reason people are not responding more vocally is that many grass-roots conservatives do not yet understand how same-sex marriages affect them personally.

That's because it doesn't affect them personally, you fucking idiots, no matter how you argue it. Commonsense people are going to realize that no matter how hard you spin it, gays marriage isn't going to affect their own marriages. Then of course, you have increasing tolerance for gays, which affects even conservative Christians.
But I think that church leaders have a big blind spot that is going to affect their abilities to get their congregations enthused about organizing to hurt gay people. Their problem is that they seem to almost think that gay people spring fully formed into the world to wreak havoc on good straight Christian lives. But gay people are born to straight people. Nowadays, when most straight people think of someone being gay, they don't think of an abstract idea, but they attach that word to the faces of friends and relatives. Yes, even conservative Christians. They are trying to organize people into a campaign of discrimination against their own brothers and sisters, nieces and nephews, and even their own children. That's why there's no enthusiasm for it.