One problem (out of many) is that the first stage just doesn't go that far.When their Texas launch site is operational, they *might* be able to land the first stage in Florida, if they can get FAA clearance and convince the residents of the Keys that a 15 story rocket stage falling towards their houses at supersonic speeds is perfectly safe.
Florida is ~1600km from Brownsville, TX. They normally put the barge about 350km from the launch site. For yesterday's launch where the first stage flew farther than normal and didn't do a boost-back burn at all, they landed around 650km out, still not even half the distance they would need to cross the Gulf.