Answer
Points within Hawaii are closer to the equator than other places in the USA. Points on the equator are the farthest from the spin axis and therefore have the greatest tangential speed (see page 134). A launch from near the equator provides the biggest boost to a rocket.
As seen from above the north pole, the Earth looks like a turntable spinning counterclockwise, and Hawaii is closer to the rim than any other location in the USA.
