The Monastic Archer Stance feat says "When you select this feat, you become trained in the longbow, shortbow, and any simple and martial bows with the monk trait."
Except there aren't any bows with the monk trait. Are there plans to include some later, or give a way to apply that trait?
Future proofing. Things don't need to already exist or be specifically planned for abilities like this to account for them.
Most likely the intention was to gather information on how monastic archers with normal bows are received and perceived then tune the eventual monk bow based on that.