Making that assessment is a part of the surgeon's job.

Perhaps they realized at some point that many patients are enthusiastic for the procedure before it's done, but most grow to hate it afterwards -- and blame the surgeon for having done the procedure to them.

Any given patient will have had zero prior experience with complex physiological and psychological post-operative outcomes, whereas surgeons do (individually or collectively.) It seems fitting that they should share that, and discourage patients from having procedures if outcomes are mainly bad.