The Parshendi burned or tore down a few, I think they mentioned chasmfiends sometimes wrecked them (and during the big chasmfiend hunt it did smash the bridge with people on it), and I'm sure that over six years, the highstorms ruined or damaged a few bridges. But not enough that permanent bridges were abandoned.

Soulcast stone bridges would be stronger, and you could make them as wide and as thick as you wanted. It would take time and gems, sure, but over six years, it should be pretty easy. And if they were camping on multiple plateaus connected by Soulcast rock, they'd want to mark where the bridges were, to make sure no buildings got put on top. And I'm sure they'd have to repair damaged bridges. But it seems like a better idea than wood bridges.