If you have 2 servers que times go up because you essentially have now split the player base. And then comes the issue that why wouldnt they just split the regions entirely...because if NA east only plays against NA east and vise versa whats the point of having them both on the same rank bracket. You would essentially make diamond or whatever without ever playing people on the other server which really isnt fair. Those are the reasons i can think of.
Also they said EU has more because its alot more people in a smaller area so they needed 2 to deal with the spikes when literally everyone is getting on. Where as the US is much more consistent with people getting off about the same time the next set get on.