Some of us realized that a crusade against Aurvandil was useless. Why declare a crusade you can't fight? And we already knew that we couldn't fight it.
To set a precedent. And because there was !@#$ you could do: fund the crusaders. It's what D'Hara did when it didn't want to fight itself, to back up its allies, on two occasions I believe. Also, it would have made stuff like Luria Nova backstabbing D'Hara instead of helping out extremely unlikely. Same with Asylon's backstab of Terran. 'cause, if a crusade had been called against Aurvandil, then the northern states wouldn't have been allowed to tolerate anything that reduced the southern states' ability to crush the enemy. So even if Morek and Astrum can't really send troops to Aurvandil, your wealth and diplomatic weight might have been enough to compensate for Aurvandil's cheating.
I agree with the stuff about Aurvandil though, but that's Rabisu's fault. Most of the Elders currently in power had lobbied for a crusade against Aurvandil as well.
Most of the elders might have supported a crusade, but the Church did not.
As another said, the cracks were forming for quite a while. It wasn't just this crusade that formed them all. It's cracks after cracks after cracks, with then a great blow from a sledgehammer.
There are just too many diverging opinions and agendas in the church. Not calling a crusade against Aurvandil, for example, was probably perceived as being northern-centric by a lot of southern faithful. "Oh, these guys totally deserve a crusade, even more than some of the previous ones who were declared a crusade against, but it doesn't suit Astrum and Morek's agendas so we are left alone to be persecuted by those heathens!" Picking your fights is one thing, but when you start sacrificing a portion of your membership, because the conflict wouldn't be fun enough for another portion of your membership, then you aren't doing what's in the best interests of the whole, you are just considering the interests of the portion of membership that's closer to home.
Plus, as SA grew in power, you got more and more people who just wanted the perks but didn't care for any of the obligations. "Hey, I just need to sign up and never actually do anything, sure, I'll join if it makes me eligible for top titles!" And the ones in other realms "Hey, if a few of us join, then they can't say we are closed to SA, and we get to follow their communications and steer things our way! Sure, we'll join!" or the like. If you don't actually ask anything of anyone for a while, sure, you can pat yourself on the back for the large number of followers your religion has grown to. But how many of them can you rely on to make sacrifices for your causes? To actually obey your commands? I think the eldership assumed too much. Authority is like a muscle: If you use it too hard, it'll tear, but if you never use it, it'll grow weak.