I don't think decrim feeds crime syndicates. California has had decrim for cannabis for a long while now. Dealers can't really make money selling cannabis because it's already so cheap at dispensaries. Most of these dealers move to states where cannabis is still illegal. In a way, dealers are not monetizing "drugs" -- they are monetizing security.

Cannabis is extremely cheap to manufacture since anyone with a bag of soil can easily grow several thousand dollars worth of plant material. The real cost is in securing the product and transporting it to the customer. In states that have decrim, the police don't even bother arresting people with cannabis because catching people running stop signs actually yield more money for the police department. There's no money to be made transporting the goods because the risk is so low.