Originally Posted by Action Jackson
It's actually very easy to understand why it's easily the most popular sport in the world. It's easy to play, most skillful sport since no hands being used and the most important thing the cost factor makes it accessible to everyone.
I think this is the most important point
To play football, all you need is a ball and some makeshift goalposts. That's why it's so popular, especially in third world countries...
To play tennis you need tennis courts, which are properly maintained, else the ball will bounce all over the place, tennis racquets, tennis balls, good shoes etc... In Australia it costs $15 dollars an hour to rent even the shittiest tennis court and you obviously have to provide your own gear. With football, you can buy a decent ball for $40 and use the free stadiums all over to play with a bunch of people.
Football isn't necessarily more exciting, but it's a lot more affordable, which the main reason for its huge popularity.