I am not sure it would make much difference to the OP, though -- there would still be kids in her house eating mac & cheese in lieu of shrimp stew, even if they were eating a bite of shrimp stew at the table and filling up on mac & cheese either before or after the meal. It seemed like their diet was the issue, more than their behavior.
PP here, and I'm not the OP so I don't know what she's thinking, but I think I get the gist of it. In my family, growing up there was a culture that we would all sit down and try what my mother made. My brother was picky about a few things--he never really liked green vegetables or salad so my mom always had a fruit salad, and he didn't like cheese very much so my mom avoided things like mac and cheese and scalloped potatoes and typically served bread with the meal so we wouldn't starve if there was something we absolutely wouldn't eat, but in general it was a pattern that we sat down as a family, tried a variety of foods, and my mom was not a short order cook. My sister-in-law doesn't have this culture at all in her house. She gets pizza, McDonalds, microwaves a TV dinner, or gives her kids a hot dog or frozen chicken nuggets. They typically don't eat at a table, they sit in front of the TV and don't necessary all sit down as a family and eat at the same time. My husband's family was the same way growing up. When her kids are out of the house, my nieces generally eat chicken nuggets. I can see how this "culture" would be annoying to someone who is used to having a family meal, especially if the kids don't want to sit down and at least try the food and behave politely at the dinner table, even if they are picky.
My younger niece has some medical issues that have led to feeding issues, so I understand that my SIL is happy to get her to eat at all, and she gets most of her nutrition from a feeding tube and pediasure anyway, so I get that she is very lenient with that child and just happy to get her in the habit of eating at all. But my older niece has a limited palate largely because she has been catered to her whole life, and my SIL doesn't expect her to like anything "adult" so tells her she won't like it before she'll even give it a try. I get that much of pickiness and taste preference is inborn and much of it is luck of the draw, but meal habits and what is and is not considered rude is cultural. Also, there are a lot of cultures where children's palates are a lot less limited than typical American food--of course people point to the French as a prime example, but I think this is true of most European and Asian cultures. I have trouble believing that the vast majority of cases is due to sensory issues and other things out of the parents control that are severe medical issues. It certainly is for some children, but probably not most of the cases we're talking about.