Because none of those are realistic. What is the point of risking poisoning yourself to ransom hostages with radiation? A gun works much better.
Leverage as what? A threat? Again- a gun is more effective.
Who wants to hold a population hostage? And who thinks a bit of medical grade radiation will help them do so?
Dirty bombs are mostly a myth. Anyone that would want to use one would get much more effective use out of a conventional bomb. Plus it's a lot easier to obtain and has less personal risk. I mean they could kill everyone that went into the bathroom where they hid the material. Or they could blow up the whole building. You might find radiation scary but explosions are far more devastating than a small amount of radiation plus way easier to achieve.