Criminalizing is a big part of this problem. With "medical" weed you can carefully chose a fitting strain just to your liking and condition, like indica for calming and sativa for inspiring effect, in hundreds of nuances even. But no. Too much money to be made for some groups from this prohibition. Can't have that, denied.

The equivalent is alcohol being prohibited leading to everyone drinking 180 proof smuggled moonshine that makes you go blind.