Adding an observation to what
@Bobby said (re: retention), I find it shocking there is a >2" stack of certification cards at my LDS that students never picked up..... is this partly due to the initial experience?
Interesting observation indeed. I had two co-workers take an O/W course, paid for by the company, and then both said they would never dive in the ocean again - only for work in (very) confined water. I asked why, and they responded that neither felt prepared to conduct o/w dives on their own. In this case, the initial experience was "bad enough" to deter them from ever gaining more o/w experience. However, the shop got their money and the agency got their numbers.
Even before I was actively teaching, I was proud to be part of an agency whose motto was (and still is) "Safety Through Education". Thankfully, the agency capitulated to market pressure with regard to O/W courses long after I stopped teaching, but maintains a higher standard (broadly defined) in advanced courses such as the leadership and technical specialties. I'd really like to say that the brand of instructor matters, but for O/W, it likely doesn't really matter that much. My wife took an O/W course, and I sat in - and aside from terrifying (for me), it did prepare me for what I would need to mentor her on.
I feel bad for the folks excited about trying scuba diving only to be disappointed by the actual experience of an O/W course. For the more motivated, there are ways to ensure a more positive outcome - as several here have suggested.
In terms of an agency, some are trying to mass-market scuba diving. However, I doubt it will ever have that kind of appeal - it is expensive, physically demanding, and requires some academic understanding of where you are and what you're doing, and commitment. Personally, I'm okay with the high drop-out rate - because if all those unclaimed C-cards were being put to regular use, I'd never get a parking spot at the dive site!