It's just a matter of efficiency. It's (usually) faster to drive from CA to Red Hook than to motor along the entire south coast of St. Thomas, saves fuel and hours on the marine engines, and frequently that can be a rather rough patch of water and not much fun for folks who may or may not be boaters and used to such rides. Or to put it another way, let the taxi cabs do what they can do, use the boats to do what only a boat can do.