It's not just that. A lot of people, including politicians, truly bought in to a lot of the anti-drug propaganda.. and many of them are also in religions which consider drug use sinful. For many of them, their opposition to drugs comes from the same sources as their opposition to gay marriage and abortion: their churches and religious leaders.
What's been incredibly interesting, however, is how their attitudes have been changing once people started to become aware how helpful psychedelics and cannabis can be... to mental and physical health, and to spirituality.
Lots of people are hurting, and the medical and mental health establishments have failed so many people. Even church prohibitions are having a hard time standing up to that, especially if they have a sherd of compassion for those suffering and those than can be helped with these unjustly illegal substances.
Big businesses today tend to not innovate themselves and instead expand into new markets via acquisitions, but how many pot business owners do you think are interested in selling to those megacorps vs running their own show and continuing to make bank?
I'm sure the DEA is fighting it as hard as they can too. Same with the police union lobby.
I do think it'll happen in the near term, probably faster than people expect just like with gay marriage. Though I also think there will be a few holdout states.