In the context of eating, why greed? If that sounds like a silly question perhaps you're taking that for granted. The reason for being greedy is for the pleasure, right?
Pleasure is not just the icing on the cake, but the cake itself.
The icing on and around it, plus the other frou frou decorations is the bit we are most conscious of so it's what we notice most and think of as the all of pleasure.
Without the underlying substance that we don't feel, because it basically just stops us feeling like kaka, we would not be able to scale heights of ecstasy and joy.
When life events press upon this basic everyday pleasure, our will to live can start to be lessened or eroded. Most normally in the form of what can become clinical depression. That can cause the body to use its available levers to stop or stem that drift.
Appetite, changing your tastes towards more sweet or fatty food and hunger can increase, energy seems to not only to have some kind of anti depressant or emotionally stabilizing, effect in terms of intake and reduced output, but also, fat tissue in your body seems to be part of that support too, something that is rarely alluded to.
The bit idea is eating lots is automatically about pleasure but it may be about making up for a lack of pleasure.
Another thing about pleasure is it's a bit like energy (maybe it is energy) there is only so much of it that can be had.You cannot go on eating and gaining more and more pleasure that doesn't make sense. So those who assume this have some explaining to do about why anyone would keep eating for increasingly lowering returns if pleasure is their drive and goal.
It also has cycles. Sex is the most obvious and clear example to look at, because it tends to be more distinct than most. There is the bit where you become aroused, like becoming hungry, the bit where you have sex or eat and the latter part where you have an orgasm or reach satiety.
There is some kind of limit, if there is an inability to reach that height, it is likely to be some kind of malfunction, rather than the "joy" of just carrying on until its uncomfortable, with a sense of something missing.
Far from being simple, eating more than you require "for pleasure" doesn't strike me as making all that much sense in the way it's been 'explained' to us.
Once you are satisfied, or achieve satiety the urge should cease, if you tried to carry on, if you could manage it, all you would normally gain is discomfort even outright pain. You might find yourself sweating profusely as your body desperately tries to use this unwarranted largesse, see Spurlock, PJ James and other media whore feeders.