Why do Call of Duty games use such minimal internet data?

I got a Telstra Mobile Prepaid Wi-Fi modem, and bought 3 GB with it so start off with. Before I bought it I did some online research and was told by many sites that call of duty uses minimal internet, like only a few MB's every few minutes. I slightly believed it would be low, but not just a few MB's every few minutes. Anyway, I bought the prepaid modem and used it for the first time last night. I had the modem next to me on the couch monitoring it at the end of every game, and it did indeed only use about 10 MB's every 15-30 minutes. I was playing for a good solid 2 hours or so, and only went through about 35 MB's. I now believe it is true that it doesn't use much data.
Can someone please tell me WHY Call of Duty uses such minimal Internet data? This isn't for a fix or anything, it's just that I'm really curious, as I played Minecraft at my mums a few months ago (IU live at Dad's) and that used about 11 GB in only a few days!