Comment by KingMachiavelli

This is a very CA specific problem cause by the fact that legalization is done at the state level and not federal.

Illegal CA cannabis production supplied a huge fraction of total US demand.

Legalization worked in that it is now harder to smuggle illegal cannabis to surrounding states legalizing (and there might be a stronger push to actually find and catch smugglers now).

Also in a high tax state such as CA a lot of 'black market' prices might be skewed by individual growers selling to their immediate friends, etc. This would not translate to other drugs because they don't grow on uh weeds.