Why are the maps designed with so much open space? There's no obstacles to force you to get off your horse and play the objective. Cav in Warband sieges were mainly used as a way to rush to a siege ladder. The one use for cav outside the castle walls is the guard the catapults and hunt down enemy cav trying to harass attacking infantry but once the gameplay moves inside the castle I think it could be designed in a way that makes infantry the preferred option.
I've seen some posts about this before but not so much about disabling cavalry entirely. I honestly think that sieges for example would be significantly more fun if there were strong cav and archer limits.
The whole concept of a siege just isn't enjoyable with so much cavalry. The attackers can go as they please without being punished really.. In warband this wasn't much of an issue. Calalry was feasible but mostly or in the courtyard or outside the castle but not in the passages etc..