While monetarily the subscription is stupid expensive, several years ago blizzard added a way to pay in-game gold for an item that’s worth a month’s game time.
If this person is putting off eating to play they’re would be considered “hardcore” in my opinion. And if that’s the case, they probably have way to get around the monthly cost, or they could have bought mass time all at once on discount.
This is probably seen through rose tinted glasses, but Halo 3 had the best multi-player experience I think. It has community created maps, game modes, and an a way for anybody with a account to share what they made. From pictures to custom forge maps. I have nothing but fond memories of the experience. So it makes sense to me at least that some people wouldn’t stop playing until Microsoft or Bungie or whoever made them.