The same reason you and everyone else overlooked McCain's associating with a questionable character?
It doesn't matter, that's why. McCain's guy is actually about three times as insane. It's been far too long so I won't be able to find it, but I recall a video of another pastor who actually knows Obama's pastor talking about him and it made a lot of sense. Naturally, the MSM would never cover that, so most people never saw it.
In the end, religious fanatics are dumb. Who cares what they have to say? Most of the time people simply blow right by them without a care in the world, but because it was a perfect smear tactic to harp on one in this instance, that's what happened.
Besides, Obama quit his church because of this mess, if you weren't aware.