Economic sanctions might work as a sudden shock action.
Long-term sanctions are likely futile. There's a point at which the domestic economy compensates. They buy from other players, they learn to do without, they grumble and suck it up, but it doesn't evoke a reaction anymore. I also suspect the tendency to roll them out as "we're sanctioning 13 specific people in the cabinet and their companies" in waves until we finally actually impact everyday civilians doesn't help-- it's basically saying "brace for impact" to the population.
I suspect there's an entire generation or more of Cubans and Iranians who just grew up assuming "this is our economic normal" and don't really see it as a direct call to action of "if you'd be so kind as to remove your leadership, we'd buy your products."
Now, if you spend as much time as possible getting nations to build and maintain deep economic ties with each other, THEN pulling the plug suddenly and boldly, can have an impact. There's more disruption and a clear inflection point.
I also suspect that a lot of civilians view sanctions as non-actionable because there are usually limited and absurd requirements for them to be lifted. I can't imagine, for example, any way Cuba or the DPRK gets out of sanctions without explicitly discharging their current leadership. At best, that's intrusive and insulting to a sovereign nation; at worst it's cheering on civil war and strife. The Iran nuclear deal, before it imploded, was a potential breakthrough here-- we gave them tangible, realistic milestones that could be achieved without a coup, and honoured the commitment.