I dont think all doctors have a bad handwritting.Most of my friends either in medicine or dentistry,they do have a good handwritting. In fact, few of them have the most beautiful hadwritting I ever saw. Me also do have a good handwritting. Except it's not always consistent especially in a rush.Like exams.Like having someone's waiting for you.etc.etc.
So, my point is. It's not that they cant give a good handwritting. They were actually purposedly did that so nobody can understand and copy their handwritting and make another copy of the prescription. You know, some drugs can give you an addiction. And people are getting smart nowadays.Who knows right?