What is it?

For some reason League Of Legends is the only game I tired to break away like uninstalling it, so I could use my time more productively, but a day later I come crawling back to it and reinstalling it. What's the addictive factor in this game that makes me wanna play more and more? Even when I haven't slept in about 2 days and my body just wanna crave more league time and nothing else.