Why do Assault get less ammo if they pick 2 weapons?

From the word itself, "ASSAULT", they are fighting on frontlines. They should carry as much ammo as possible they can carry. Imagine fighting on frontline and you are not ready and running out of ammo? It's understandable for Assault if they carry more guns and ammo.  It is their job. Remember, their weapons can't fire continuously just like LMG as they also need to reload so why is the developer giving them less ammo?

What is the logic of depriving ASSAULT standard ammo? Is the developer telling Assault players to fight together with other class and not to fight on frontline? If they would get less ammo, it shouldn't be more than 20%.