I'm sure the cost to over cater in economy is probably very minimal, and on average when people miss out it's generally no more than 20 or so. My last flight however we had a group of school kids, and they all wanted the pizza meaning a lot of people missed out, but something like that is a one off.
Not only is over catering extra weight, it's extra space required too. And mostly it is such a waste when there is already so much waste as there is.
I understand the disappointment. I experience it too when I travel and while a little disappointed myself I can accept it as part of traveling. Even as a crew member I can miss out on my crew meal choice (can be up to 4 choices depending on the port meaning only 2/3 choices of each).
