Football is an outlier in the sporting world. It shouldn't be as large as it is; it is a statistical outlier, after all. As the world's largest sport, it has around 3.5 billion individuals who consider themselves fans of the sport - over a billion more than the second most popular sport, baseball (cricket).
The Champion's League is the most sought-after competition in terms of clubs’ football, and the reason is pretty darn simple: it’s the pool where all the big sharks meet. Not that they want to meet each other, really; the thing is, as the pool sizes reduces, the small fish has already been eaten, and the biggest will need to fight each other.