How does saddle nose happen after rhinoplasty if only thing that was done was rib cartilage was placed over bridge?

1) Is it because rib is too short so causes depression between top of bridge & tip of nose? 2) If not, what causes depression in that area? 3) Can saddle nose cause internal valve collapse thereby causing breathing problems out of each nostril? Can’t breathe out of each nostril separately 4) Currently Dr filled w/ filler but I want to know the cause. Also the 1in long rib cartilage still slightly sticks out w/ filler. Filler is not long term. Would like long term solution.