Every name you listed there was a political fanatic. I don’t mean this to be dismissive, because, that is one kind of assassin, but they’re not professionals.
Those are people who have a political message and were willing to die to get attention. (Oswald’s a little of an edge case there. But, the basic idea stands.) These are people who wanted to send a message. That’s completely different from someone who is paid to kill a target and disappear.
Someone screaming “Sic Simper Tyrannis!” before taking someone’s head off, is a very different breed of killer from the kind that sits in an office building and takes a single shot before vanishing.
We’ve talked about assassins at length before. There’s a classification of types, a further discussion that dips into avoiding detection and discusses the difficulty inherent in actually researching real assassins, and a suggested media list that should also serve as a primer to other things we’ve written on the subject.
To be honest, I’m not sure what else to say on the subject, that we haven’t covered already. Though, we probably should do a piece on the psychology of terrorists and fanatics, but that’ll have to wait for another day.