I'm 38, my parents are mid 70s and when I was a kid loads of people had burgers, nuggets etc, so unless you're in your 80s or older I don't think this is true.
I've got very little skin in this game op, my son, although "picky" actually won't eat nuggets, burgers, sausages or fish fingers. His favourites are pasta dishes, mushroom pizza, beans, scrambled eggs and mushrooms with toast and vegetable curry. He does love chips and birdseye vegetable fingers with tomatoes sauce though 🙂
I did and still do eat burgers, fish fingers sandwiches and even potatoes waffles sometimes though - I'm not unhealthy or overweight. I ate/eat those things in between other meals like roast meat and veg, pasta, stir fry, curry, eggs, casserole, risotto, paella etc.
Sometimes it's not being able to cook, sometimes it's money or time being scarce, sometimes it's issues with getting kids to eat just anything, often it's a mix of all those things.