If you are mentally not stable, if you are not a stable weight, if you are on multiple treatments treat cancer etc..if you have high expectations, if the surgeon feels he can not or hasn’t got the skills to proceed with your case and when that is the case they usually suggest a surgeon who they think will be able to give you best results, there are other reasons like a present infections etc..hope this helps and this is my own knowledge from what I’ve been told and researched