Our portion sizes are too large and we're a consumer culture. There's also an element of not being wasteful and "eat everything on your plate" as a thing of honor instead of eating until you are full. "Starving kids in China" etc. My special needs son will eat anything you put in front of him, especially vegetables, but is good at stopping when he's full. But if you tell him to eatmore, he will. Plenty of times we've had to correct my mohter in law for trying to make him "eat all of his fries" No. He's fine.
We have too many restaurants and other eateries and they have to compete with each other. Even when I was a kid 40 years ago eating out was a rare thing. I admit it myself, I get lunch on Tuesday from my favorite local deli, a breakfast on Friday morning from our bagel place. We go out as a family most Saturdays, and when I visit my mom on Sunday I get her Taco Bell because she's 95 and needs to eat something hearty and their power bowls are good for her. I walk across the street to KFC and get a chicken sandwich. Mobil apps are awesome. But now we have door dash and uber eats teaching young peole they can get anything they want whenever and it'll cost more but they've normalized that cost. So they're being wasteful and unhealthy for a barely warm meal from Chipotle.