You've not read the "data". You've made a selective choice to ignore evidence. Below I used WebMD as a source, there are other uses but this is a decent accepted usage list.
The first reason is for chronic pain, and doctors who prescribe it do it so they are not addicting their patients to opioids. Below is a list of "other" options, only one of which is your "one reason".
https://www.webmd.com/pain-management/features/medical-marijuana-uses
Doctors also may prescribe medical marijuana to treat:
Muscle spasms caused by multiple sclerosis
Nausea from cancer chemotherapy (this is the "one thing" according to your "exhaustive" research)
Poor appetite and weight loss caused by chronic illness, such as HIV, or nerve pain
Seizure disorders (this can be amazingly effective, you should watch some of the videos)
Crohn's disease
Now, you can be prescribed an extract from MJ in states where MJ is not legal, but according to those who have had it prescribed it is not nearly as effective in the treatment of those conditions as a simple joint and the joint is far less expensive and doesn't involve enriching the same company that made epinephrine so expensive.