I would bet another advantage of wood is they fail gracefully.

From article:

"We had one ladder here that was fully involved in a fire for 25 minutes, and the whole tip of it—six feet—was crispy. It looked like a log you pull out of a campfire," Braun says. "That can't go back in service but we were curious, so we put a new halyard [rope used to hoist ladders] on it for a load test. Even in that condition, it passed."