I bought map packs before for Halo games and Call of Duty. But then I never really played those games. Outside of shooters, now that I think about it, I haven't really bought any DLC. I'm not really for that, we'll add missions to games you can buy later; which is the LA Noire method.
After watching an Extra Credits episode; though, I see that it seems that many of these companies do it to get profits lost due to used game sales. Obviously, that's only a small reason, but I can kinda understand that situation; I honestly just never thought of that before.
I still don't love the concept of DLC.
Edit: Let me clarify, I don't like how DLC is done now with a single thing at a time. I wouldn't be terribly opposed to the idea of expansions for games (PC games have done it for years). Why not just create far more than one thing or separate things to get it all at once?