It's been awhile since I read the book (maybe I should re-read) but from what I remember, while domestic production is possible (and probably still happens to a small degree), it mostly dried up because it's soooo easy to import it to Mexico and truck it up. Or, in the case of the OP link, import the precursors, put it together in Mexico, and truck it up. Like, as a drug trafficker, you'd be a fool not to from a risk and financial perspective. It's literally not illegal in China.

Whether this is an "opium war" is another question. We never would have had an opiate crisis in the first place if not for the Sackler's aggressively pushing prescription opiates. Or if we had, you know, the social will and character to actually treat chronic pain and drug addiction.