Why are uber prices different during different times of the day?

Other answer:

Gerald:
That's their whole pricing model. If there are more rides wanted than drivers available the prices increase to encourage more drivers to come on duty.
Ricki:
Supply and demand. Prices are cheap when no one is using the service. When everyone wants a cab then the price goes up.
DR + Mrs Bears face:
Hi Taxi fares have always been different in the unsocial hours of the day.
Jack:
Supply & Demand