Except there have been catastrophic floods in Appalachia - Asheville was struck by one in 1916, Appalachian Kentucky in 2022, and numerous examples in between. It’s just been that they don’t occur in the same place so it’s not a compelling risk in the practical sense especially in a budget constrained area like Appalachia. But heavy concentrated rain in mountains is bad and flooding can be catastrophic. And climate change has increased the number of heavy rainfall events.
There’s never been an avalanche in New Orleans nor is it conceivable in any way.