The purpose of airline food is not to feed people but to show that the airline cares. The small plastic boxes with different food in each are a pretense of a multi-course meal. Multi-course meals are considered fancy. If the goal was to feed people, then a large sandwich or a bowl of pasta would be logistically simpler to provide and eat, cheaper and more filling.
Similarly a day of service (of volunteering) of some organization is not designed to help others but to show that the organization cares. The organization wants to be seen to be helping. If educated employees go and clean the park or work at a soup kitchen, it is a waste of their talents. It would be more productive to do their regular work and donate their salary to hire cheaper labour for the simple volunteering jobs. More volunteering output (cleaner park, food for the homeless) would be produced. Division of labour increases overall productivity, as Adam Smith pointed out.
Volunteering by highly qualified people may make sense if it is a vacation for them – their enjoyment outweighs the productivity loss relative to the efficient arrangement where everyone does their specialized job. A different type of work is a break from routine, which may be restful.
Once I participated in the Yale Day of Service. It was supposed to last from 9:00 to 14:00, so more like a half-day of service. Many people were late, so we started going towards the worksite at about 9:30 and reached it in ten or fifteen minutes. We were supposed to clear the underbrush among some park trees. The tools were dull gardening shears. The work ended at about 12:30. One person with a motorized trimmer could have done in ten minutes what twenty people with shears did in two hours. Clearly the goal was not to clear the park of bushes and weeds, but either a social event or a show of caring. Namewise, Yale Two Hours of Service sounds less nice than a Day.