Another list of reasons dictators in brutal dictatorships are the most secure.
A brutal dictator will retaliate very hard against your family and community if you target them. If someone targets the pope or president, they get put in jail. They are not tortured, their children is not tortured, their grandparents are not tortured, etc. There is less to lose by killing a president vs a brutal dictator because mostly you just lose your freedom. You and everyone you care about aren’t horribly tortured and imprisoned for life.
Dictators are willing to hide behind human shields. Even if you target a dictator, he isn’t above hiding in civilian homes and using human shields, which would offput a lot of military units sent by democracies, as well as some criminal elements who do not want to kill women and children. Bin Laden was hidden with tons of civilians, which was a reason he was not targeted with a drone strike (a drone strike killing dozens of children would look pretty bad) and instead a hit team was sent in. Bin Laden wasn’t a dictator, but you get the idea. When Saddam was on the run in Iraq during the 2003 invasion, one technique he used was he along with a few bodyguards would pick houses at random, go inside and drug the owner(s) until they passed out. Then they would sleep there and leave the next day. People are less likely to target a home filled with and near civilians. If someone wanted to kill the leader of a western democracy, that leader does not hide behind human shields which would off put a lot of assassins.
Dictators have dozens of palaces, so you have no idea where they are.
I’m sure there are other reasons. But which dictators in which 3 countries? I don’t know. I’m guessing Kim Jong Un is one. No idea beyond that.