I think an important distinction is that drug prohibition often works in terms of specific chemicals by statute. E.g. drug X is now illegal for use and distribution.

Securities fraud law instead works in concepts and intentions and is fleshed out by case law. E.g. did the seller give the buyer sufficient information for the buyer not to have been defrauded?

A better analogy to securities using chemicals would be poisoning. The law doesn't need to catch up to specific chemicals; if it's evident that you wilfully, or recklessly added a poison to someone's food, it's illegal, and it doesn't matter how you did it. If it turns out that some ingredient is unknowingly toxic and the whole industry was adding it, then it's difficult to argue criminal intent. The SEC is more like the FDA, than it is the DEA.