I bring snacks an protein bars when we go to cons

Convenience, mostly. Either they're too young or new to realize that con food is overpriced and usually bad, or they don't care because it's convenient and sometimes they like it.

Lots of people have fun just eating the convenience store sushi and con pizza, and many cons try to get themed food too; the one I was just at had the venue cooks make (admittedly subpar) mochi and onigiri.