I have an alert that the forum group Cash Shop Custom Wears has disbanded... I get that the group is no longer there, but why would this happen?

The owner probably disbanded it.

Whenever you get that notice it means the owner chose to ditch it. It could mean the group wasn't active enough for them to keep and they didn't have someone to pass it to. You could always remake one yourself if you desired :)

Thanks guys! I'm sad that it's gone, it was very helpful, but maybe someone else will start one back up. :)