[tedsanders]

Florida and Puerto Rico, alternatives considered by SpaceX, have locations even closer to the equator than Texas. And non-US locations have options far closer to the equator. Being southern is good, but other factors are important too.

[vonmoltke]

Florida is closer, but the possible launch sites are not. Still, both those sites and the Texas site are far enough south that, as you say, going further south doesn't buy much.