To the best of my (also limited) knowledge, there is no reason for brushless motors to be more current-hungry than brushed motors, in fact the opposite, it is simply that the motors currently available are sold on the basis of their high power output, for the boat/car racer types and model fliers. I have two small brushless motors in a couple of planes, each appears externally identical, but on the same battery pack, one is a low-revving, torquey motor and the other is higher revving. Each is suited for its particular purpose. Perhaps there is simply not a strong enough demand for low-revving, efficient brushless motors for scale boats to make them a financially viable option for the manufacturers?
Having played a little with larger brushless motors a few years ago (in model planes that would take a glow engine of .40-.60), I can assure you that low kv brushless motors do exist, but that good ones are not cheap.