my son asks the crew shortly after takeoff (sometimes before) if they could please check to see if they have any kit kats loaded on the flight. They get a kick out of that and always seem to leave him extras during their cabin walk thru's. (sorry 'bout that!)
I, on the other hand, want a Lindt dark chocolate bar in flight. Often have to force myself to stay awake until the basket is first put out, versus sleeping until the basket just has the leftover fruit/chips.
Another reason for a shortage: I have seen multiple crews either set aside or poke open sealed snack baskets (taking most of the chocolate intended for the next flight!). then several kitkats/lindt bars got slipped to YYZ jetbridge workers on arrivals. Quietly handed and pocketed. We said something when the Service Director doing this the last time and he expressed his frustration. He said they expect this treatment by now for getting the jetbridge here quick. If the chocolate mafia at YYZ is skimming off the top, AC may not be under-catering at all.
(public service announcement: Canadian Kit Kat chocolate tastes much different than American Kit Kats...2 different mfr's license the brands. Try the Hershey's USA kind sometime and you won't even want an AC Kit Kat!)