Cavalry became more common because the people that were creating the “discourse “were usually family members of the Calvalry, since knights and the educated beurocrats were both younger sons of lords , and it was in good form to hype up your brothers accomplishments on the battlefield, hype up your family name. This also shifted focus away from arming /training the infantry of your armies, for fear that if you taught your infantry how to kill enemy knights, they might eventually try to kill you when the when the peasant infantry got upset at your mistreatment of them. So what happened was a sort of arms race, with each sides knights continuing to bulk up themselves, the size of the horses, and their combined armor in order to attack other knights, since infantry couldnt be allowed to, while the infantry was able to fight other infantry because they both sucked equally
