My mum's family was always poor, & did 9 wedding receptions for 9 daughters.Despite not always being able to afford generous portions at home, when they catered for guests they catered in abundance. My S-i-L, from a similar background, is the same.
When mum or S-i-L or in fact any of the extended family cater, it's a standing joke there will be 3x as much as we can eat. It doesn't matter, it's packaged up, sent off with guests or with big families, there's no option of things going to waste.
I've been to wedding receptions where, being among the last to go up to the table, there's just been crisps & dips left. If that was my reception, I'd be so shamed.
I think it's the old-fashioned value of hospitality, getting it just right is impossible so too much is offered. When it was home - catered, that didn't mean waste. Now with catering companies doing it, & people's appetites varying drastically, there are going to be times when there's lots left. I think for a big "do" that's absolutely fine, no reason still why people can't take "doggie bags" home & there is the option of taking some things like salad stuff to the community shop.
There's always waste when people are eating out on a regular basis too.
For a big do like a celebration party, in my view that's more acceptable than the mass of food thrown away by companies catering things like corporate / sports events.