i’m 90% sure the reason why the spear is not avaiable on foot knight is simply because it would become a dominant pick. It’s already really good on Huntsman because of stagger temp health alone. Now on Foot knight, with his push talents, insane attack speed, Extra stagger talent and on top of that, him having Stagger Temp Hp… i dont know, would possibly become op, specially the stagger temp hp + more stagger power.
A argument against this is that his ult already has enough crown control, so bringing a exclusively crowd control and anti-horde weapon would be reduntant, as it really doesnt do much besides that. But it could potentially invalidate shields to a certain extent (shields would beat it only in the push capabilities, foot knight however has his ult for elites and the spear has insane crowd controll and horde clear, probably making it more valuable).