I'll talk about alcoholism because that's what I know.
I never understood why I couldn't control or get a grip on the amount I drank, why it felt like I needed more after 6 hours of drinking than I did when I started.
It wasn't like an appetite though. If I am hungry I'll eat until I'm full. Then stop. Or if I am being greedy I will eat more than I need. Then stop because I feel sick. Probably regret it and wish I stopped sooner but I will still stop.
Alcoholism was more of a need, which I could never really justify or explain after the event. It became a priority and came before everything else as a basic need that I could never really satisfy.
So not greed. More of a bottomless pit that I kept trying to fill.
P