Unfortunately, ill-advised budget cuts mean that even here in the Netherlands (a country with a lot of surface water) swimming is no longer a standard part of the school curriculum in some municipalities (it used to be pretty much mandatory).
I've known people who volunteered to go to various islands to teach basic swimming skills who also haven't been able to quite figure out why either.
https://www.csmonitor.com/World/Making-a-difference/2017/082...
https://alexischateau.com/2016/11/08/10-things-you-probably-...
It just seems bizarre to me.
I probably went to the sea (the Atlantic, in France) and played in water every other day or so during summer and autumn for most of my life until I had to move away as an adult, but that didn't magically teach my how to swim. I had to learn later. And I still hate swimming.
If you live next to the sea, you're going to be spending time around and on the water. It follows that you should learn how to survive in the water if something goes wrong. What if you get caught in a rip, or if someone else gets in trouble in the water and you have to help them? What if you're in a dingy and it capsizes?
A significant proportion of people couldn't swim 250 m or tread water for 10 minutes.