Whenever I teach an OW class, I ask why the people are getting certified. At least half of them say because they are going on a vacation to an area that has scuba diving, and they wanted to give it a shot.I think a better question might be: why do many people stop diving a few dives after the OW class? What can be improved in that transition?
Whenever I do a refresher class for people who have not been diving for a long time, I ask a similar question. The two most common answers are 1) I originally got certified for a specific vacation, and now I am going on another similar vacation, and 2) We started a family and had no time until the children grew up.
For others, I think the primary reason can be tracked to instruction. A lot of people are trained to dive overweighted and on their knees. When they go to their vacation dive and struggle to swim comfortably while neutrally buoyant, something they never had to do before, they don't have a lot of fun. If they have fun, they will continue.