Because it's pointless when you could just take a 11B and spend an extra week (if that) teaching him the fine art of steering a missile or driving a Bradley, and give him an ASI or SQI which identifies him as having a special skill that's not really justifiable as an entirely new MOS. The Armor CMF teaches every Cav Scout how to both drive a Bradley AND utilize TOW and Javelin missiles in the span of their OSUT regardless or wether or not the trooper ends up in a light, airborne, air assault, wheeled, or mechanized unit. Infantry does the same since neither are that colossal of a task. This way, Infantry only has to worry about recruiting, and training 2 MOS's instead of 5 or 6, and then filling 6 MTO&E tables. Wether one agrees with it or not, its much more streamlined.