Although one would assume the upper nobility were just as keen archers as their assorted clients, in the typical fashion of warrior aristocracy with nomadic connections. Similarly one would assume the catas' arm defenses in particular might get in the way of effectively wielding a bow, so the weapon would not be the central focus of their battlefield tactics but chiefly an useful option to have along.

But personally I always assumed separating the "archer catas" from the otherwise similarly equipped pure shock types was just a way of getting around the game's restriction of only two weapons per unit... Ie. the two types represented the essentially same type of warrior merely acting in a different battlefield role, as with the Hypaspistai/Pheraspidai split.