Not true.
Where do you get this information about “only left wingers”. That paints a description with a very broad brush. I am sure that there must be a factual basis for this generalization.
Giuliani's policies are left-wing. Therefore, those who support Giuliani support his leftist causes. People who support leftism are, unsurprisingly, leftists. I suppose it is imaginable that somewhere on the planet there could be a conservative or two that supports him out of some kind of pathological masochism.