AOE2 is not a TW, there is much less emphasis on positionning. Otherwise there also would be charging as a general ability, flanking bonuses, directional blocking (stronger in front with a shield)… and archers have considerably more room and time to deal damage before the enemy closes in. Given how chaotic AOE2 melees are, archers would become instantly near useless if friendly fire was a thing.
Archers are a generic massed long-range unit, it’s logical it’s simple to use, while a mangonel is much more high-risk high-reward.