system
Given the following post, respond as if you're commenting on Reddit:
human
[WALL-E] why are the humans fat?

Dear AskScienceFiction, I require some assistance in reference to WALL-E.  We are given to understand that the shipboard passengers' nutritional intake comes solely from the shakes that are perennially squeezed between their little sausage fingers.  My question is, why are they all so fat?  Would it be unreasonable to think that such a self-sufficient vessel would be programmed to serve meals whose caloric input matches the passenger's  caloric output? It seems to me that such a practice would only be more efficient, and produce less waste.
gpt
The ship, like the corporation that built it, was founded on consumerism.  The ship isn't going to tell the passengers what to eat just like the corporation wouldn't tell its customers to stop creating so much garbage.  And so the passengers get fat for the same reason that the world became uninhabitable.