It has always been a matter of efficiency in data service. Much like the fabrication of a commercial airplane, the design of the server side of a service like World of Warcraft affects what can be provided to the players for as long as that service is being used.
With an airplane, you can conceivably add more seats inside. You can squeeze more people in there, to a point. But you can't (easily) expand the hull to make room for more seats. Over the long run, if the airline wants to accommodate more people, they add more planes to the route, or replace an existing plane with a larger plane that has room for more seats.
This request - which is heard loud and clear, by the way - is like asking the airline to simultaneously increase the number of passengers that can be carried on every plane in their fleet. Can it be done? Absolutely. It may be something that we are able to do, and soon. It may not be, because providing reliable data service is extremely important to us.