Because your standard orc just isn't awful enough.
Level 5 Troop (humaoid)
AC: 22 (19 dismounted) PD: 19 (17 dismounted) MD: 14
M: Spear – +10 vs. AC, 18 damage.
16+: Sweeping – deal 9 damage to all Engaged enemies beyond the primary target
R: Spear – +10 vs AC, 20 damage. Useable once per encounter.
Steppe Cavalry: The Orcish Horse-Lancer can move twice as fast as a foot soldier, getting to Far distance in a single move. In addition, the Lancer can make its attack at any point during a move, freely disengaging and engaging opponents once per round as needed.
If a player character hits a Lancer with a natural 18 or better, that character can choose to forego the normal effects of its attack to dismount the Lancer. The Lancer takes 15 damage and loses all benefits of the Steppe Cavalry feature. In addition, its AC drops by 3 and PD by 2.