Why does Nissan recommend that you change the rotors when you change brake pads?

It could be that in their opinion the rotors will wear out before the next service, so to avoid the inconvenience of you coming in again just to have the rotors replaced they have recommended they be changed with the pads. But you should ask them why the rotors need to be changed, for instance, are they warped, or perhaps they’re worn-out. Have them tell why instead of just accepting it.