The only reason I've heard is that some nurse thinks the patient will get a false low reading and they will take sugar to fix it, and make themselves sick.
Personally, I think that's bull. It's important that every diabetic person should have their own meter, and any doctor who thinks it's unnecessary is a waste of time and money, and should be switched out for another.
My doctor gave me one a couple years ago, when my diabetes was still controlled by diet and exercise, because even though I wasn't on meds, he said I needed to be able to monitor it.