The amount of work it takes to become even halfway proficient at swimming is way above the other two. And if you haven’t even had any formal swim instruction until a young adult you can pretty much forget ever being in the front pack (or even the next two chase packs). Being able to run great and swim well is the sweet spot because anyone can learn to bike well off those two.
Well said! I live in a ski town and I always compare swimming to alpine skiing. My twins (11 years old) have grown up skiing. If they didn't touch skis again until they went on a spring break ski trip in college, it would take them about half a day to be back to where they are now. With swimming, if a runner swam summer league when he was 10-13 and if he did a few years of middle school swimming with a good coach, and then didn't really swim in college, some of that feel and awareness of the water would be in him as an adult. Someone smarter than me with science could probably put some reasoning behind this. I just have seen it play out with athletes. Teaching an adult to swim is like teaching an adult to downhill ski-- it can be done, but can take a long time!