Settlements may not send their militia if they consider it suicide. In this case, the vampires aren’t attacking them but you, some mercenaries, so it’s not really worth dying over.
LOL! I can just hear the militia captain: “Now’s a good time to break for lunch … and be sure and close the gates!”
In a single player game, there's no such thing as cheating. It's merely "creative manipulation of the default settings"!
