why would caliborn's god tier outfit not fix itself afyer john rips it up?

Little shithead doesn’t deserve a full cape.

In all seriousness, likely because he hasn’t died? Like, God Tier Healing is Resurrection, not a Healing Factor. The only thing that grants a Healing Factor seems to be the Ring of Life. So if we’re going by the Clothes -> Body Part comparison, the cape ripping is just a wound. It’s not lethal so there’s no repairing.