Why are [airline meal](https://en.wikipedia.org/wiki/Airline_meal) portions so small, even on long-haul flights ?  
Sometimes it's not even enough for children, let alone adults.

I have some assumptions, but I would like to submit this question to those who are in a position to know the genuine reason(s).

[![img][1]][1]


  [1]: https://i.sstatic.net/AwJ7n.jpg