We have discussed this before. Certainly for the check-in staff and FAs it became a logistical nightmare with many cock-ups, and third-party charter operators would either not be able to handle it or not even be told.
That said, charging for the meals, even partially, coincided with a notable uprating of the standard, and hot meals are the norm again. There must be some here who remember that charter flight nadir, "seatback catering" of the 1970s/80s, where the refreshments (cold, inevitably) were placed in special compartments in front of you which you could eat when you wished. These had many practical problems too. The meals for both legs were loaded in the UK, the one for the return leg was meant to be locked up until released during the turnaround by crew with a key, but too many outward pax with a couple of hours to kill and a second meal tantalisingly in front of them found a way with coins etc to get at it. Likewise early boarders would grab their neighbours supplies before they arrived. There are no easy solutions !