> Is the opposition to cannabis as a therapy at least part rooted in the fact it is not patentable?
The IP is certainly fuzzy but that's no argument. If it can be commoditized and involves some form of creative/innovative work, there's pretty much always some way to create legal protection for it. Besides, just because there's potential for competition doesn't mean that people won't try to enter the market.
> Large Pharma can't make enough money from something people could grow themselves?
As the article itself explains, growing weed is not simple. A sophisticated operation requires a lot of resources and dedicated man-hours.
The primary reason that no big, entrenched players are moving on it (or that anyone who does it hasn't gotten too big) is that the fact remains that marijuana is illegal. (This is true in a lot of countries, not just the U.S., but the rest of this comment is going to be U.S.-specific because I don't know the situation in other countries nearly as well.)
No matter what the states say, federal law overrides state law, which means that anyone that grows pot has huge legal exposure. There's also a secondary problem: pot growers have a lot of trouble using the kinds of services that are traditionally available to businesses, because B2B's (1) want clients that are not at risk of getting shut down by a DEA investigation and (2) do not want to expose their own businesses to legal risk, which they would be by working with a pot-growing op.
There's a lot of stories about dispensaries in Colorado who are denied, for example, banking services, because of the litigation it would expose banks to.