Because it is "not sanctioned by the sate", as you put it means their behavior is not that of the free market. They spend resources moving products via secret means, for fear of being thrown in a prison and their cannabis taken from them. This causes them to put time and energy into doing things that aren't needed, like building tunnels that are hundreds of miles long, instead of using a road.
This causes this economy to function in a completely different way than an open economy.
In a normal economy, if you buy bread from a bakery and that bread is horrible, you stop going to that baker. Because drugs are illegal, it means that competition is highly limited. Instead of anyone being able to learn and grow cannabis and providing competition, you have a very select view able to do grow and distribute the drug. This creates oligarchies, which are what you listed above. So because it is illegal, the state has created a drug oligarchy and it functions as such.
You mention the silk road, another good example. Not everyone has the skill and intellect to use the deep web and avoid government crack down. Most people do not even know what an IP address is, let alone how to scramble/hide it. So while there are free market aspects to the silk road, it is much harder for someone to learn how to function in that business than in a store setting or legal online website like ebay.
You are also talking about one market place. All buyers can register for free on the Silk Road but you have one organization controlling who the sellers are. So SR is still quite closed, as an economy goes but it is a better example than the others you listed. It still suffers from many market altering effects due to federal government law. An example of this is the same as above. Some have the ability to grow in their homes, assuming they have the room and access to the knowledge and materials. Not everyone can grow safely outside and just the added fear of having your entire life destroyed because you are growing a plant completely distorts the market.