If that's really the end of his dialogue tree, it's pretty annoying.
I'm pretty sure I've reached the end of both Jacob and Grunt's trees, but everyone else, even after the mission is finished, apparently has better things to do. Well, Jack is confused about the relationship between her and Shepard, and Tali is somehow confused about the fact that Shepard isn't interested in a relationship with her, but whatever. Miranda's filing paperwork, Samara is meditating, Legion is building consensus, Mordin is coducting mad science for fun and justice--which I approve of--Thane is being emo, Zaeed doesn't count, and Garrus is performing calibrations.
It can't be the number of missions performed that inspires the characters to open up to you, as Mordin was a constant companion, and Grunt only got to tag along for his loyalty mission. Perhaps certain dialogues are unlocked as you gain levels?