There is, I think, a few things that contribute here.

I don’t think there’s a single objective answer.

The gist would be that it’s habitual due to long term cultural patterns, the same as what any given culture has in regards to food.

At some point, the concept of big piles of food being the default crept in. I suspect that it originated between feast/celebration foods and the “working man’s meal” where early workers in agriculture and industry needed a shit ton of calories to keep doing their work. Once enough people see that kind of portions often enough, the mind decides that must be what everyone is supposed to get on their plate.

Then, as things like machinery and eventually robots removed more and more of the physical labor from jobs, sizes never went back down because the outcome of eating beyond what you need isn’t immediate and obvious. So you follow the defaults, do what you have seen and internalized as the norm.

But there are still plenty of jobs where loads of calories are necessary to get through a shift. So people still see that, and thus expect it on their plate even if it isn’t a healthy amount for the job they have.

TV just follows society most of the time, so a show will most often mirror a norm without any effort to correct for what’s best for individuals.

When it comes to restaurants, there’s an extra later though. Even if people know they don’t need that much, there’s an expectation that if you pay for a given order, you’ll get the same amount as anyone else that orders it. So restaurants have to scale to what at least a decent sized segment of the population expects to see. They won’t be happy if they get less return on their plate compared to another diner, despite that other diner being on a road crew busting their ass laying pavement in the sun all day and needing more.

If a restaurant either changed sizes per customer needs, or charged an extra amount for people with higher needs, they’d go out of business fast

Statistically speaking, yes. American portion sizes are larger than European and Asian countries but I dunno…

I’ve been served a whole table of food in Italy and ate for four hours chit-chatting with locals. Korean’s put so much food on the table there’s no room for drinks. In Vietnam I’ve been served a fried fish the size of my thigh in the best curry sauce ever. Order Schnitzel from Germany or Austria and you’re getting a pice of fried meat the size of your chest on top of a mound of potato’s and lemons. Loads of places in China serve family style, even if you’re traveling alone.

Every country has its big plates but that doesn’t mean you can’t find reasonably sized plates. A McCheeseburger is the same size round the world. You also don’t have to eat your whole plate in one sitting. Get comfy with leftovers and you can save a few bucks on your next meal.

Also, don’t believe what you see on TV. Those dudes say some WILD shit and most of them are riding the influencers train to try and dig up customers. The bigger the spectacle, the more views on the tickytocky.

No wonder why they have a higher rate of obesity

To be fair, this isn’t just about portion sizes, it’s about what’s in those portions. We have a ton of heavily processed, wildly unhealthy food options, and they’re all the budget friendly ones. Getting things like fresh fruits and vegetables is much more expensive than it should be, so we have this weird situation where it’s possible for someone to be both food insecure and also overweight, just because the food they do get is so unhealthy and fattening.

From the 50s to the 90s, the US was in a massive wealth and growth cycle, and people demanded value for their money because the consumers had the power.

That value was provided by large portion sizes for low cost, which normalized the idea of eating a large amount of food for every meal.

Now we’re just sick and obese and used to it even though the nutritional quality of the food has dramatically plummeted.

Because you work so long that when you get the chance to eat you have to get it all in at once.

But, y’know…freedom or something