The game is so addictive because you get drawn in by the potential of what the game could be. Unfortunately the balancing is terrible and the match making is awful. They need a placement system which re-evaluates players skill every few months(which can be done in short seasons which placement games determining ranks) because games have players of different levels of skills and it tilts a lot of people. Due to this and the fact some champions are really unbalanced have created a really toxic community as it makes people angry and then they take it out on each other.
Yet people still play because they can see how the game could be good if things changed. Riot need to get their priorities straight and fix the fundamental things but instead they spend their time making new skins so they get more money from people.