Because it can transmit analog voltage signals (such as the input 1.1V and its output may also be 1.1V), similar to a short route (but the on-resistance is somewhat large and frequency dependent).
Low frequency analog voltage signals such as audio can be gated with this device (a single power supply using AC signals need to pay attention to the addition of direct capacitance and bias voltage), rather than just 0, 1 digital signals.