One reason soccer is so popular is that it is very easy to play. Unlike sports such as American football or basketball, all you really need is a ball and an open field.
So, why is soccer the most popular sport in the world? There a lot of factors that should be considered, but easily the most important one is soccer's decentralization, meaning that is played globally instead of just in one region. Other factors like its low cost to play and simplicity, significantly contribute to making it even more popular.
Sports, in general, awaken passion in people, but there are a couple of things that make soccer different from other sports like baseball, basketball, or American football that make it significantly more popular in the whole world.