I do understand that is just my case, but it seems that I have smaller ears (and consecuently, smaller ear conducts) than the average person.

I cannot wear the Apple earphones because they don't fit firmly: they're moving constantly (which generates noise that I hear) AND they tend to fall from my ears, even just sitting down in my computer and moving my head slightly.

I would love to get rid of the cables, but airpods would be even a bigger problem, because at least with the cord they won't hit the floor.

I usually employ in-ear earphones, which come in different sizes and that resolves my problem.

TL;DR: it's not only sports/exercise, there's people with smaller ears :)