Legalization of marijuana would cost the for-profit prison industry billions of dollars in lost revenue, hence why they spend millions fighting against it.
Rauner in Illinois kept it off the list for medical marijuana because if Vets don't have to use tax dollars to purchase expensive meds from big Pharma, that money doesn't leave the taxpayer's coffers into Pharma's pockets. His ALEC/Koch buddies stand to lose quite a bit of funds.
I doubt I'd ever risk taking it myself due to my alcohol addiction, but I'd sure love for it to be available to anyone who needs it.