so addicting

Because, LoL. This game is such a Riot. It's Ezreal as it gets.

The sunk cost fallacy contributes a lot.

It has high replay value. Why are sports still interesting after playing the same game over and over again? It's a very interesting, dynamic system, with lots of room for mastery and outplays, which, tbh, are one of the most satisfying things to do in a game - you just want to do them again and again.