One of the biggest drivers towards higher potency is ease of smuggling, which is a lot less of a concern for legal manufacturers. They’re also ripe targets for wrongful death lawsuits so there’s an incentive to keep the potency within reasonable limits unless the drug is relatively harmless. They can also accurately dose their drugs and make large pills, making it harder to accidentally overdose on doses that are measured in milligrams

Getting sued for overdoses typically prevents behavior like that.