I'm not surprised that they would, sounds like what most kids would do. That's why the buffet has to be curated, so that the easiest way out / path of least resistance isn't just "empty calories". So limit the offerings. And maybe use approaches like the Maya Method [0] to "trick" them into thinking what's commonly regarded as work or chores, to be fun. It's not easy, but it can at least be tried.
[0] https://news.ycombinator.com/item?id=17905657