Its pretty simple, they don't give out prices because lots of their prices are sky high. If they give prices over the phone many people would simply buy elsewhere without setting foot in the store.
Sounds like a car dealership I worked for once upon a time. I made a ton and never gave out a price until the customer said they would take the car home that day. It is all about getting top dollar.
I can see no other reason a retail establishment would withhold prices instead of advertise them.