I think that reason soccer is so popular overseas, especially in poor countries, is because the convenience of setting up a game with limited resources.
Besides a soccer ball, not much else is needed.
A couple of 2x4s can act as a goal posts, and young legs can burn a lot of energy in urban settings with nothing else to do.
I wouldnt exactly call the UK, Australia, New Zealand and Western Europe "poor countries" and soccer (or "football") is #1 sport.