Why does the traveler say that the passions still survive?

The traveler, who sees the shattered statue of the once great king Ozymandias lying on the desert, says that the passions the king once felt still survive because the sculptor who made the statue captured them in the carved face of Ozymandias.
Ozymandias's passions can be discerned from his

frown, / And wrinkled lip, and sneer of cold command

The traveler leaves it up to the reader to decide what passions a frown, a wrinkled lip, and a sneer communicate, but certainly Ozymandias does not come across as a happy, friendly ruler. One might imagine instead an angry dictator used to belittling and bullying other people and being obeyed.

This impression is reinforced by the statement Ozymandias has carved on his statue, warning the people who see it and his mighty kingdom ("works") to feel despair, presumably at how puny and weak they are in contrast to his greatness. Of course, the irony or contradiction is that for all that he is trying to generate terror and awe at his great strength, nothing is left of Ozymandias or his kingdom but a broken statue and empty desert sands.