Right, because he wouldn't want to put himself out for an imperial citizen, even after having won the civil war.
You just don't leave your people at the mercy of the Thalmor if you can do something to prevent it. That, and Tullius saying he's going to send Ulfric's and Galmar's heads to Cyrodiil, I found really distasteful.
It was also distasteful how Ulfric treated Tullius before his death, yes he had a right to kill him but he could have been more respectful about it, Tullius gives Ulfric a last request. Also at the end of the legion quest Rikke says "talos guide you" to Ulfric, You know Tullius hears it, instead he just says "What was that Legate?" Ignoring the fact that she said something ilegal.