[cronix]

Yes, it's because there is a large black market in states that haven't legalized it and in a lot of cases, they're selling it cheaper than the stores where it's legal. The state sanctioned growers all have to have their products tested in labs for purity, pesticides as well as percentage of THC/CBD. The stores (separate entity) also have heavy regulations and security requirements as these are strictly cash businesses (since it's still federally illegal, you can't use federally regulated banks, or credit cards). It's expensive to do so. There is also quite a high state tax on cannabis sales. Illegal growers don't have any of that. It's also a lot simpler to cross state lines than international borders as most states don't have border checks. I know California does to check if you have fruit on board (large agricultural state trying to prevent various pests/diseases), but out of hundreds of trips across the border we were only actually inspected once and that was likely because we were in a camper so they couldn't just look in the window and see.

As a different example, there are "dry towns" where alcohol sales are illegal. The bordering bars where it is legal do very well.