Although it is a bit strange from one point of view - the richer a Roman citizen was, the more he could spend on his panoply.

Hastati were presumably poorer than Principes. But a sword is a more expensive weapon than a spear. For that reason, it would seem to make more sense if the Camillan Principes were the swordsmen, rather than the Hastati.

However, tradition may have influenced the choice. The older (and richer) a Roman citizen was, the less accommodating he may have become to military reform. In the Servian period, the older and richer citizens were spear-armed hoplites. Maybe it was easier to persuade a young Hastati to give up his spear and retrain as a swordsman than it was an older, more experienced Principe? While the Triarii, the oldest men in the legion and the ones that kept the hoplite-style armour longest, also kept the spear longer than either the Hastati or Principes.