Riker didn't want
to be Captain. I think there are numerous times throughout TNG where he gets bumped up in rank and Frakes plays it like the whole "responsibility" thing un-nerves Riker (which is odd because Riker's whole point in the beginning was that he had fire in his belly for a command of his own). The truth is that Will found his niche in life and was perfectly comfortable as XO. It was pretty clever how the writers actually used this as the basis for the plot in "The Pegasus" though. Having Riker question exactly when and why he changed from ambitious career man to just being a guy who is happy being where he is.
(Admittedly, in any real
situation Riker would have been busted down for standing in the way of other people in the chain of command. Again, BOBW gets some great dramatic milage out of this.)
Tbh I think even in "Nemesis" Riker seems less than enthused about leaving Enterprise and becoming a Captain. The sweetener was really his marriage. Not that one necessarily follows the other.