Maybe it's just that I don't eat at restaurants a huge amount in the US and I mostly eat at better restaurants when I do. But I travel to Europe quite a bit and I just don't see the stark difference.

Yes, a lot of restaurants in the US will have a fair bit of filler (potatoes/rice/other vegetables) in a typical main course. But if I have fish and chips or a steak pie at a London pub, I'm probably not going to finish all the chips and other vegetables there either. I'm not sure I've just about ever looked at a main course in Europe and thought to myself "Oh, what a small portion."

And my experiences in Germany, the Netherlands, Belgium, etc. are similar.

I do agree that when you get out of major cities in the US, food options can be pretty limited. Even where I live, about 50 miles outside of a major city, there are only a few places I eat at or get takeout from on anything like a regular basis and I wouldn't like to subsist on food from them 7 days a week.

I find food is a lot better on the coasts too. If you're in the middle of the US, unless you're in a large city, the food is pretty abysmal.

That's probably generally true although I've also stayed in smaller towns in places like northern California and meal options were pretty limited there too. A problem is that you can devolve to fast food chains pretty quickly and the local options aren't necessarily any better. A good (pricier) restaurant in a small town probably isn't really supportable by just locals.

For the me the stark difference comes from the plentiful supply is extremely low quality food. At the better end of the food quality scale I think the US and EU are comparable.

But when you look towards the bottom end of the food quality scale, the bar for saleable food is just abysmally low compared to the EU. You simply can’t buy food of such poor quality here. As a consequence the average quality of food in EU is substantial better, not because the EU produces better food, but simply because it doesn’t accept the low quality stuff the US is happy to eat.

That may be the case. I basically never eat fast food aside from the occasional local pizza place or maybe a food truck. This is true whether at home or traveling so I don't really have a comparison scale at the low end.

We’re talking about different national cultures and their approach to food. Your personal preferences aren’t the most relevant.

I split my time between the US and UK. If the food options in the US are "appalling" relative to the UK, it makes me wonder what parts of the US you've been spending your time in.

Food and cuisine in the US is highly regional, and varies immensely. In the part of the US where I currently live (Pacific Northwest), the local food is much healthier than is typical in the UK and higher quality. Portion sizes are not uniform across the US either but I would agree that on average the UK is significantly smaller.

I wouldn't characterize typical food in the UK as particularly healthy, it reminds me much more of the diet you see in the Rust Belt of the US. The relative dearth of fresh, high-quality vegetables in the UK is particularly noticeable for people that have lived on the west coast of the US (which has amazing fresh vegetables generally by global standards).