Locality/size of routing tables. If you had a hundred million subscribers with fixed IP addresses moving all over the country, you essentially could not aggrega

Locality/size of routing tables. If you had a hundred million subscribers with fixed IP addresses moving all over the country, you essentially could not aggregate any routes, but would have to have a hundred million routes in your routing table, and/or you would have to push all the traffic from and to all subscribers through one central router, which in particular would add latency for any subscribers that currenty are at the other end of the country.