One thing I think you are missing about Big Pharma is that they have everything to gain in the federal legalization of cannabis, because with the help of "common sense regulation" by government, they will be the ones with control over the production, distribution, retail of, and profit from it.
To say they do not want it legalized because it solves problems that their other drugs are supposed to solve, is plain incorrect. I can assure you they will not care if you treat your anxiety with Prozac, or you treat it with their marijuana and it's derivatives.