I love this question! Because I ask this myself all the time... you see, I've already played multiplayer games (league of legends, Hearthstone even red alert 2)... but I've never stayed for more than two or three months.

In this game it's different, I've been playing for half a year and I just want more and more...

I think part of the reason this game is so great is because the battles are short and don't take much time, so even on the busiest days I can play and relax a bit and have a fun (and earn a bit :)).