OP
Well, the oft-mentioned History of NAUI has at least a partial explanation for both. Each made critical decisions made back in the day about their approaches to attracting students.
YMCA: It should go without saying, first of all, that the YMCA is not really a commercial enterprise like a dive shop, so it would never be interested in sponsoring travel, even if they thought it was a good idea. According to the History of NAUI, the YMCA decided to focus their instruction through dive clubs, with the idea that dive club activities would create a need for new students. That didn't happen. The YMCA program eventually ended.
NAUI: NAUI was formed by the people who had led the Los Angeles program, a taxpayer-supported organization. When they wanted to go nationwide, they could not so so with taxpayer funding, but they wanted to stay non-profit. That was a problem. In the early years they relied heavily upon the backing of a skin diving magazine to replace the tax-based funding. They had their headquarters in the magazine's office building. When that source was sold and went away, they floundered. One year they survived on a large loan from Bill High, who later created a tank inspection company. They decided that the best way to attract students and funding was through universities. If students could simply select a scuba course instead of some other physical education course and thus pay for the class using tuition money they would have spent anyway, things should work out. They didn't. One critical year (as will be explained later), they decided the idea of going national was not working, and they decided to pull back and focus on California. Reflecting on it in the History of NAUI, the founders saw their earlier approach to funding and attracting students as a tactical error.
Others: When NAUI decided to pull back and concentrate on California, they canceled a major instructor training session scheduled for Chicago. This infuriated the Chicago NAUI group, so they logically created their own agency--PADI. Seeing that the NAUI funding model was not working, they looked for another approach. At about the same time a skin diving (as it was then usually called) retail association, the National Association of Skin Diving Stores (NASDS) came up with a different approach. The writing does not clearly identify which happened first, but both PADI and NASDS decided that the only way scuba instruction could survive was to link it with retail sales. NASDS changed the last word of its name from "stores" to "schools," and both organizations made scuba instruction a part of the retail skin diving market. The idea was that by interlocking them, each supported the other. NASDS is now SSI, as a result of first a merger and then a buyout of the SSI ownership.
