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.