Third, one can never convince an entire populace to rebel on property rights alone. It is clear that what upsets the Nords most is the infringment on their culture and their worship of a person they consider a god being made illegal and punishable by even death in some cases. Ulfric takes up this cause. If he is not devout, he is insincere about one of the major reasons for leading the rebellion. And that ties back to what so many NPCs say about him.
It seems that freedom to worship Talos was Ulfric's initial motivating factor. Whether it still is could be debatable. Igmund offered it to him as payment in Markarth, and so far as we know, nothing else was asked for. Once the city was taken, there was no talk about him continuing to lead armies around or making moves for additional power. He stayed there until the Thalmor and the Empire forced them to reneg the deal and arrested him. The priestess of Talos in Windhelm notes that Ulfric often comes in praying for strength. Quite a long bit of work to keep up a facade.
