You can't blame the Hollow Men for being dissatisfied. They are trapped in the desert on the bank of a river they can't get across. In fact, you would expect them to be even more ticked off than they are. But quite frankly, they can't even muster the enthusiasm to complain. They try not to say anything at all. (When you don't have a proper soul, it's harder to get worked up about soul-crushing misery.) The Hollow Men are like the souls in Canto 3 of Dante's Inferno, who are so bland and cowardly that they are excluded even from the fantastically grotesque torments of Hell.
Questions About Dissatisfaction
How much do the Hollow Men understand about their own condition? Do they recognize the extent of their own unhappiness?
Did God punish the Hollow Men, or did they get what was coming to them? If so, of what does their punishment consist? If not, isn't being ignored by God a punishment in and of itself?
Do you think the Hollow Men suffer more from their physical condition, or from the knowledge that they cannot enter Heaven? How much do they know about Heaven?
How would explain the reference to their "lost kingdoms" in line 56? What kingdoms did they lose?
Chew on This
The Hollow Men do not realize how unhappy they are because they do not understand the joys of Heaven enough to know what they are missing.
The Hollow Men understand the joys of Heaven at an emotional, but not an intellectual, level. Thus, they are deeply unhappy as they intuit their damnation but cannot explain it.