Team sports generally support larger numbers of professionals. In part because viewers are simply watching more people at the same time, but also because teams need redundancy.
If you're stepping away from organised activities, practically every kid in the world plays football, all you need is a ball, clearly that outnumbers sports that need equipment - Tennis and especially Squash.
By that metric Tag is probably the most popular sport.
Anyway you need a ball, several people, a goal, and a large open field to play something vaguely close to soccer. So it’s popularity varies wildly by area.