@kensuf,
While I will admit that I am pulling this from a dark orifice, I do believe that one reason why some people do not continue diving is that they subconsciously know they are not skilled enough to dive autonomously. At least in areas with dark, cold water like the Puget Sound. My basis is that my retention rates have flipped from the times that I taught on the knees and followed agency guidelines for dive planning versus teaching neutrally buoyant/trim and augmenting the dive planning information.
I do believe that 5 hours of pool time and 4 OW dives is sufficient to create competent, confident open water divers if they are taught properly.
I agree that a 3 day course could develop competent divers, but only under ideal circumstances. Students that are already comfortable in the water and have an aptitude in the activity, and minimal ratios (1:1 or 2:1).
Having personally taught literally hundreds of 8:1 and even 10:1 pool sessions to college age kids during my 10 years of teaching scuba at UF, there's no way I believe I would be capable of consistently getting all of the required skills to mastery and develop competent divers with just 5 hours of pool time while keeping 8:1 ratios. BUT, at UF we always had 12 weeks of pool time.