Securely storing information about a driver's trip on that driver's phone is hardly "offloading their costs to society." I assume the driver does not want the information about the trip they are providing to be lost, and therefore that they do not get paid, if an Uber data center goes down. This is not about storing all of Uber's data on the driver's phones (this would make no sense), only the information for that particular driver's activity.
Further, as the article describes, this may actually be more reliable than separate backup data centers.
Further, as the article describes, this may actually be more reliable than separate backup data centers.