1. People like movies where mutant monsters lay waste to a city.
2. People like vigilante movies where some law-abiding citizen is pushed to the breaking point by one outrage too many while the cops stand by, and wreaks brutal revenge against those who have done him wrong (or her).
3. It follows by an ineluctable process of simple geometrical logic that people will like even more movies about a vigilante city that sets out after the perpetrators after its Sister-city in Japan is trampled flat (again) by Mothra or Ghidorah or Megalon, leaving a trail of dead monsters behind (and let's face it, these creatures are all in cahoots so it doesn't really matter which one you kill, amirite?).
(1) Title changed to appease needy pedants.
(2) In comments tigris points out that an alternative choice of lead actor would allow us to use the title "City Come A-Walken".