I think it is a very simple answer for this one.
Football doesn't need loads of equipment, all you need is a ball and to make some goals or posts. This means it is open to the poor communities as well. They are not restricted by having to buy things in order to play. Young children can play barefoot and dream of being a star.
The sport is so commercialized and is on Television in every country. Thee is a big marketing budget which FIFA handle and it reaches all corners of the globe. When the world cup is played it is the most viewed sport in the world attracting huge audiences.