The reason you don't legalize drugs is because you don't want the kind of people who engage in major drug trafficking to suddenly be granted access to legitimate political and economic power.
Dominance in their core competencies allows them to run mediocre-to-bad agriculture and logistics operations at a huge profit, because any potential market competition in those sectors is suppressed by the law. The only ones who could meaningfully compete with a cartel at coca-growing are another cartel.
If the law stops suppressing competitors (and instead starts protecting them), organizations which are good at bribery and violence no longer have an edge.
Instead it would be sold in Walmarts Pharmacies, and they would make 10% just like they do with much else they sell.
Once a power dynamic emerges, it becomes difficult to undo it until it is too late, and individuals become statistics to be used as evidence for repealing legislation that made such a power dynamic possible.
It's laughable that people think you can just "join" the elite, like if you have enough money.