In most sports, you have a world championship every year, meanwhile, a World Cup happens only every four years.

When you have screens and stuff setup by the city to follow a World Cup, the crowds are not made of die hard football fans, the majority of people there are normies that don't give a hoot about football during the 47 other months of a WC loop. Here we call them "footix". If the WC was happening every year, they would be bored and less and less of them would come out to the public events. Meanwhile, making it only every four years, they have time to forget that they didn't quite enjoyed it, they can believe things are very different from last time, and they agree to reserve part of their mental bandwidth to the event. They wouldn't do this on a yearly basis because they fundamentally don't care about football. They want to enjoy sharing a unique experience surrounded by friends, family and random peers. You can't do this every year because it removes the special character of it.

To illustrate this further: here we have the Tour de France (cycling), that happens every year, so no scarcity. Unless a stage passes near you. Which is something that happens even less often than a World Cup. In that case, people with no interest in cycling will go to the side of the road and go crazy.

Soccer is the only important sport so it gets all of the attention

Soccer gets all of the attention so it stays the only important sport