This is a great point. China's attempt is a great example. They can shut down exchanges, but Wechat channels pop up offering escrow type services, and boom, the market is back in business.
It's impossible to ban narcotics as well, but they are still persecuted.
And look how well that works. Another great example of bad outcomes from over regulation.
One is an order of magnitude tougher than the other. Meanwhile, you picked a perfect example to show how useless banning something like narcotics is; it has led to massive negative second-order effects like gang war and international strife.