Well, one doesn't just choose to be a Paladin, which is one of the most common misconceptions. A Paladin is part of an order. Before you could even call yourself a Paladin you'd have to invest time in becoming a member of that order, and part of that is indoctrinating yourself in to the faith of that order - including that faith's deity. Players who start as Paladins will have backstories that explain why they are out adventuring, very often as part of their service to the order. Multiclassing in to Paladin is a very large narrative that would require a lot of coordination with the rest of the party and more dynamic access to the game world that I am not sure a video game can accurately reflect without reducing it to "you're a paladin now!" - which might be one of the reasons they are trying to simplify it, which again I feel is to the detriment of the class overall.
