From memory, the gods of good did try to stop the cataclysm, they sent warnings that went unheeded, they gave lord Soth the chance to stop the king priest, saving the world but ultimately they couldn't stop it, the balance needed to be maintained so it was out of their hands.
While this is true, the fact is, it seems kind of short-sighted. "Ok guys, the mortals are out of control, and the King Priest has become so blindingly good that he wants to ask us to destroy all evil, which is totally against our agreement with the rest of the pantheon."
"Well, can't we just go to the K-P and tell him why it's a bad idea?"
"Ah, no, we can't directly intervene. But there's an out, we can get someone he will trust to do it."
"Seems roundabout, I prefer writing messages on the guy's bedchamber wall in burning letters of fire, but ok. Who do you have in mind?"
"Lord Soth, he's a great guy!"
"Great, wonderful, fantastic. Who else?"
"What do you mean, 'who else'? Just him!"
"Uh....now, hear me out. What if this guy gets attacked on the road by bandits, ambushed by followers of the Evil Gods, distracted by needy orphans, or finds out his wife has been cheating on him, sending him into a fit of blind rage?"
"Oh come on, what are the odds of that happening?"
"Dude. Even if
you aren't omniscient, I'm pretty sure Gilean is. Maybe we could ask him nicely if we should have another backup plan?"
"No, that would be cheating. We must trust in the Good of mortals!"
One Cataclysm later...
"So, yeah, about that Lord Soth guy..."
"Look, don't talk to me, ok? I have to figure out how to prevent the mortals from dying of famine because their crops have failed for seven years running. Dust! Dust, of all things! It's everywhere, it blocks out the sun, and it dries up the land!"
"Yeah well, that happens when you drop an asteroid on a planet. Whose idea was that again?"
"Ugh, Reorx bet us that he could use an asteroid just large enough to not wipe out all life on the planet."
"Huh. You know, it might have been better if we had. I mean, we can always start over, we got a few extra planets laying around in the crystal sphere..."