Call of Duty, Expansion Packs

Treyarch really pisses me off.  Why do they feel like it is necessary to release a new expansion pack every month?  All-in-all, I'm going to spend $80 on a game that I already spent $60 on.  Shouldn't this content be free?  I understand that they are a company out to make money, but they are taking advantage of their players.  Four expansion packs!  The last two packs were released one month apart from each other...  On the other hand, I can't wait for the new map pack!  :)