I guess you missed his point. They will BEGIN to produce those drugs once the market for pot had dried up.
There are very few places in the world where coca will grow, Mexico is not one of them. Almost all coca is grown in the mountains of Colombia, Bolivia, and Peru. They can grow poppies to make heroin in some parts of Mexico, but their yields aren't very good so they buy most of it from other places that are much more suitable for opium poppies. Their marijuana yields are pretty good. They're getting 1,200 kilos per hectare on average, a little over a thousand pounds of dried bud per acre. They now produce more marijuana than any other country in the world. They also produce most of the methamphetamine consumed here, which they don't have to grow. Without marijuana, they'll keep producing meth and just continue to import most of the cocaine and heroin to smuggle and sell here. They get it pretty cheap and after they smuggle it and get it to the towns where it will be distributed it is worth several times what they paid for it. But, total demand for all cocaine, meth and heroin consumed in this country is only in the hundreds of tons compared to many thousand tons of marijuana. Far more marijuana is consumed here than all other illegal drugs combined. They make most of their money from marijuana sales, and they aren't going to be able to increase their returns from these other drugs much because they are already satisfying almost all of the demand for them.