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

Other answer:

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.
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.
Supply & Demand