i think it's because "commercial" producers of vegetables can hydroponically raise more for less, just as an aquaculturist can raise more fish for less $...as an example, an aquaculture company started up near me about a year and a half ago.. indoor facility, with 1 wall of nft tomatoes under lights.. (just as an experiment).. they're running a ras operation, and to be comfortably profitable, they need to raise 100,000 yellow perch/year - this is a small operation, the owner, 1 fullt time guy basically running it, and a couple of part timers - the ft guy also cleans their fish, and they also clean fish that people bring in for a charge - an extra expense - many hoops to go through certification for cleaning/selling cleaned fish - one way around that is to sell live fish but you have to have or create a market.. they "dump" about 300 gallons of water a day which is pretty efficient if you see all the water that they have..the last time i talked to them they were preparing one tank to try raising malaysian river prawns
i think it's more a matter of marketing.. as you note, having the right fish would make a difference (i've seen koi going for thousands btw!) but having commercial quality veggies that you can sell to niche markets would be the key..
i'm sure there are a few "commercial" ap enterprises but i'd bet that most of them rely on other streams of income, such as seminars, training, equipment etc....to be profitable.. friendlies in HI has basically evolved to a low density system where the fish are considered an "extra"
i think it's more a matter of the initial cost at this point.. but really, to make money at it, you have to take a close look at the markets available and target them specifically.. and then look to expand that market and develop secondary income streams..