For the record I agree with you. However for fun and science. Here's a list. Gonna shoot for more than ten.
Appetite enhancers,
Dronabinol
Megestrol
Somatotropin
Opiate Pain relievers
Morphine
Codine
Hydrocodone
Oxycodone
Methadone
Fentanyl
Meperidine
That's ten, continuing.
In many cases it can replace prescription Nsaids (anti inflammatory) of which there are more than I'm going to type. (I came up with a dozen)
These are known uses, without addressing cancer treatment or any other anecdotal uses. I think it's safe to say that it has the potential to dent the bottom line but I don't believe it's "THE" reason weed is illegal.