To me I see one of the challenges from severe sanctions is that it can push a country doing anything to raise currency, any business. Without commenting on ideological motivations, it is possible that Iran has the capability to design and build these drones and they have a customer in Russia and they need business, need money due to the strangling sanctions. ie, without knowing ideologies might be that country has to hold its nose and sell against its wishes just to keep some revenue.
That does not mean I think the sanctions are wrong nor that I have the answer. Maybe if we'd taken the trouble to negotiate a nuclear deal with Iran earlier ... oh, we did and ...