The staff ate it later

It's related to the concept of Mottainai (もったいない, 勿体無い) in Japanese culture. Where any waste is considered bad, specially related to food.

https://en.wikipedia.org/wiki/Mottainai

There is a similar concept in English culture called "waste".

Yes, waste is an English cultural concept, especially in the US.

In this concept, waste is viewed as a sign of affluence.

So ironically, the more one wastes the more "conservative" one is considered to be.

Pretty much the opposite of the Japanese concept of mottainai.

The idea of not wasting food as a sort of baseline concept is a thing plenty of parents in the US teach their children.

Many Boomers may have heard something along the lines of "Many kids in Japan are starving and would love to have that food" even, bringing this somewhat full-circle.