I paint with broad strokes because having been diving with numerous AI and cruise ship divers over the years I find the vast majority of them to be less than a pleasure to dive with to put it nicely (your mileage may vary of course).
My mileage certainly varies. Many "cruise ship divers" may be infrequent divers and/or inexperienced. That's not a reflection of them traveling on a cruise ship. I'd guess that the vast majority of these people book their dives as cruise excursions and are put on a typical cattleboat operation with their fellows. I've found that "cruise ship divers" who take the time to research and book independently of the cruise usually do fine underwater. So I'm guessing your experience diving with "cruise ship divers" is limited to your cattleboat diving experiences.
Your AI generalization, however, is simply ridiculous. Plenty of divers stay at AIs for the convenience. After diving all day, it's nice sometimes to not have to leave the beautiful tropical-island facilities and deal with the crowds and noise of the city, nice to not have to decide where to eat or drink, nice to enjoy the entertainment, nice to enjoy the pools and beach that are lacking at some of the city hotels. And, depending on how well one takes advantage of the included fare, one can save money as well. It's easier to budget for a set priced hotel than to anticipate how much one might otherwise spend on food and beverages.
Another reason AIs are popular is when there's a non-diving spouse or significant other accompanying a diver. The non-diver can enjoy full use of the facilities, beach, etc., while the diver is out playing underwater. For instance, my last AI experience in Cozumel was at Secrets. Turns out another diver staying there happened to be booked on my boat. He had as much or more experience than me, was just about as well-traveled, and was an excellent diver. Maybe even as excellent as yours truly.
BTW, the characterization in your other post of rich people being afraid to walk the city streets because they equate poverty with crime is likewise silly. First of all, impoverished areas in places other than idyllic Cozumel often are more dangerous. Second, it may be that the rich people can afford a taxi, or can afford to stay at one of the AIs that you disdain, surrounded by luxury and palm trees, and therefore have no reason to walk the dirty streets of the inner city. Honestly, it comes across as envy. Spend what you like or can afford, it's your vacation, but why fault those who can afford a different sort of vacation and prefer it that way?