They want capacity to allow for new/old players, they have to as a company believe they can still attract.

To merge all the servers 2:1 really would be saying "We expect no new/returning players" and that that will signal
the end of updates as we now have them, any hope of future expansion packs.

Any company that isn't interested in expanding its product's uptake will stagnate and ultimately fail.

It can be frustrating but the npc's are a cleaver way of addressing the issue though, as long as they keep opening
areas/missions to them.