Why are so many people in their 20s and 30s such picky eaters these days?

It seems like every time I go out to eat with or cook for people in this age range, many of them will not eat most vegetables (some won't even eat most fruits), and many only like the generic fast food/plain cheese or pepperoni pizza/chicken nuggets or tenders and fries/plain hamburger/mac and cheese type of food. Won't eat anything with vegetables or seasoning.

With the way some of them eat (almost exclusively fast/fried foods, junk food and soda), I'm surprised their bodies don't revolt against them any more than they do. 🤣 Many of them act like being asked to try one bite of a vegetable is going to kill them, on the other hand.

Is this a generational thing, or perhaps just a regional thing with people I know? I've noticed this with several people in my age group that are like this.