One would think that, if all else were equal, the dive agencies that offer their academic materials for free or at very low cost would dominate the market, because dive shops that teach scuba would be looking to save that overhead cost.
In this thread, NAUI, GUE, and RAID are mentioned. I live in Colorado, which is annually among the top 3 states in the USA for per capita scuba participation, and we have a wealth of scuba shops in the state. None of those shops offer NAUI. One of them offers one class (Fundamentals) of GUE. One of them offers RAID, but the last entry on its FaceBook page announces that is July OW class is canceled and asks if anyone is interested in a class in September.
So this is an honest question: if cost of class materials is such a critical factor, why aren't those three agencies dominating the market in Colorado? I don't have an answer myself.