Addicting part, Not to down talk anyone, but, When you collect titles, guns, perks, killstreaks, unlocks it gives you something (not physical) but the game does give you something. So in your head, it is rewarding. You then forget, you are not physically gaining anything. It is a race for rank, leaderboards, etc. I like to compare addicted COD players with Tunnel Vision. As you block out (important) things and focus just on the game. Sadly, that's when the game, stops being a game.
If you or anyone thinks they are addicted; Get a calender and add up how many days you spent playing JUST COD, when finished, you should have a different outlook.