The gods of the Romans have not rewarded Roman piety with Empire--if that were how it worked the Greeks would have ruled forever, given their veneration for the gods on the stage!
Claims by the priests to the contrary through the use of augury and divination are simply false, and easily shown to be so by even the most rudimentary of methods (the chief of which being that the Empire's borders have so regularly shifted and changed, even under 'good' pagan emperors like Julian!).
And of course, we know that even the best of pagan writers (Cicero, in this case) don't really believe in either the power of the gods or the value of augury. Instead, they go along with tradition because it's what the masses demand, all the while slighting the very practices they're engaged in.