Comment Efficiency, thats why. (Score 4, Informative) 409
Science!
The mohave is hundreds of miles further away from the equator than Brownsville. The closer to the equator, the lower amount of fuel you need to reach certain orbits. The rotation of the earth adds to your relative speed, and this amount of speed provided increases the closer to the equator you get.
Why is it better to launch a spaceship from near the equator?