The parsimonious explanation is that amphetamine was basically grandfathered in over a historical period where shrooms/acid were cultural and political pariahs and they still have to overcome the residue of that a half century later.

Has nothing to do with being a one shot solution vs subscription.

Even economically the conspiracy theory against one shot cures makes no sense. As your shitty subscription solutions all go generic, I enter the market with my low risk one shot cure and eat all of your lunch.