Through continued government interference, of course. By legalizing possession and artificially keeping prices high, you end up increasing illegal sales.
Why illegal dealers are flourishing in Colorado:
-Cannabis is taxed 25% on the total sale price. This is on top of sales tax and countless other government taxes and fees. If cannabis was sold at true market value, such sales taxes would probably exceed the profit.
-Cannabis stores and growers are being prohibited from writing off expenses on their federal taxes. Imagine running a business and having to lose 30-40% of GROSS income! This is a gift to the cartels by the feds.
-The number of stores and growers is strictly limited by the government. The existing stores have high prices and still can’t keep product on the shelves. There is obviously room for market supply to grow and reduce prices but government restricts it.
-Legal cannabis is a novelty to many people. Since it is currently restricted to a few areas, people are flying cross country to patronize the stores. This keeps prices high for the locals and encourages them to continue buying from their old local dealer.
I don't necessarily disagree with that.
I assume by "cartels" you mean Mexican or other foreigners. But the Mexican cartels have largely abandoned bulky, smelly, low-profit marijuana for easier to transport & conceal, higher profit drugs like heroin.
And in places like Colorado, I'm guessing any foreign cartels have even less of a foothold.
So, I still don't see where any "cartels" are getting rich off marijuana when people can easily grow and/or sell in places like Colorado, even if it's technically illegal (but very few are getting prosecuted).