And inventory. And different inventory.
It used to be that each department store had different fashions. As such, there was a difference between each chain. However, once they all started selling the same Chinese crap, there was no differentiation so why buy ono anything other than price.
And department stores used to have inventory and more than one of each size. How many times do you need to go into a department store and find that they don't have your size before you quit going in at all?