Virtues cannot be considered passions because of a principle of movement. Passions in and of themselves are not good or bad, but they are determined to be good or bad in reference to reason. For example, hatred is referable to evil only. Remember, Aquinas said that a difference between virtues and passions is that virtues are good and passions are not good or bad in and of themselves. It seems he has contradicted himself here by pointing out that some passions are always good and some always bad.
Passions arise from the appetitive soul and are judged one way or the other by reason.
Virtues, however, are formed and maintained by conscious decisions to act in a reasonable and moral way. Thus, the movement of virtues is opposite to that of passions.