Training and genetics.

Genetics/randomness must play a significant role. When I was a teenager I could hold my breath for ~1.5 minutes without even trying. With a bit of technique I got it up to 2 minutes with relative ease, I think my max was around 2.5 minutes. The odd thing is that I had no reason to be able to do that, I was pretty out of shape, I didn't play any instruments, or have any other hobbies that would help build that kind of stamina.

On the flip side, out of all the genetic benefits one can get, this might be the lamest one. :(

I'm rather unfit these days - but as a teen I could easily do 3mins at my desk in a class. I can't remember the volume but we did a lung capacity test at school and I had the highest in the class, despite not being sporty or active at all, so I think I have genetics on my side.

I recently tried the 'Wim Hof' method, and was well over 4mins after just a few days practice, and I just went snorkelling and was able to outlast all those I went with. If I was healthier I am sure I could get longer still.

I would think that high altitude cultures with genes for handling altitude sickness would do well in breath holding contents.

Like why isn't some Peruvian on Nepalese person the record holder? Lakes too cold for recreational swimming maybe?