Why are there very few Masters Swimmers under 40?

Easiest answer: Life. Once you are done with college swimming you are onto a career, family, travel, work, home, sleep (as you get older you need more). Then you also have the "wew.... it is done" feeling after your last college meet. It took me almost 30 years to realize I missed my pool time and the sport. So, in my 50's I am trying to get back into it and also having to get over being disgusted by my times, I mean, you should get better with age, shouldn't you? I suspect many others suddenly return to swimming in their late 40's and 50s.

Easiest answer: Life. Once you are done with college swimming you are onto a career, family, travel, work, home, sleep (as you get older you need more). Then you also have the "wew.... it is done" feeling after your last college meet. It took me almost 30 years to realize I missed my pool time and the sport. So, in my 50's I am trying to get back into it and also having to get over being disgusted by my times, I mean, you should get better with age, shouldn't you? I suspect many others suddenly return to swimming in their late 40's and 50s.