I imagine it has a lot to do with access and where someone lives. How many times can you recreationally dive the same local quarry before you lose interest and maybe move on? Also, there's probably two types of divers starting out. The try it and see if I like it because it's on my bucket list diver and the try it and the now I'm addicted and it's a way of life diver.
I would think specialty divers stay in the sport the longest. Tech, spearfisherman, pros, commercial, etc. I don't know what the attrition rate is for spearfisherman, but odds are if they live near coastal towns and stayed in the sport after a couple failures and shark encounters they're probably lifetime divers. I imagine "near misses" dispatch a lot of divers.
I had the privilege of meeting the legend Ray Odor recently. Great man, gave me the tour of his home, trophies, shark tooth collection and we spent the better part of an hour trading stories. He's over 80 yrs. old and if he could physically dive tomorrow I'm sure he would. The man's been scuba diving for over 62 years and freediving longer than that. For the avid fisherman who harvests his/her own food they probably stick with it for a long time.
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Here's some cool history. Clearwater, Florida 1954.