It's also a lot easier to teach kids than adults. Besides logistical things like the ease of pulling a kid around versus an adult, by adulthood a lot of people

It's also a lot easier to teach kids than adults. Besides logistical things like the ease of pulling a kid around versus an adult, by adulthood a lot of people end up being embarrassed around trying new things, especially ones that require them to be largely undressed and in a strange environment. As a teenager I ended up carving our a niche among my fellow lifeguard/ swim teachers for myself teaching adult men to swim. I suspect it was their pride stopping them from taking lessons from the (far more prolific) girls, who often times were teaching their kids to swim.