IMHO, mostly due to history and some caution. A thoroughly oversimplified history would go something like this: In days past a lot of medicine was based on wha

IMHO, mostly due to history and some caution. A thoroughly oversimplified history would go something like this: In days past a lot of medicine was based on what seems to work or what ought to work. Unless the effect is really obviously disastrous it's easy to believe an intervention is helping even if it's not. Medical research was of course done but doctors mostly went with their gut or whatever article they'd recently read in a journal and liked the sound of. It's only since the late 80's and through the 90's that Evidence Based Medicine really started to get going. Since then doctors have (sometimes slowly) come round to the idea. However all this research takes time. What do you do about those interventions that haven't been tested yet? You could stop doing anything that hasn't been thoroughly researched, but that risks letting people die or suffering unnecessarily.