I'm honestly not sure that's true. Legalization and regulation will make it easier to grow legally, but it's hard to undercut someone who isn't paying for the land they use. This is similar to how cheap ASICs and electricity haven't pushed out botnets mining bitcoin - free is still cheaper than cheap.
Within the last five years, when a retired co-worker came through. (I guess that working on old cars didn't fill enough of his time.) Actually, he didn't offer it to me, but another guy in the office got a jar.
The problem is that, at least in Humboldt County, the legalization is designed to allow existing growers to continue to profit, while preventing new comers from getting started.