You went to the wrong parts and ate the wrong things.
I used to live in Paris for a spell and the food here in San Francisco is better. California has some of the freshest and best local produce in the world. If you eat at real restaurants (not McD), and intentionally buy fresh food (which is available at normal grocery stores too) then you're getting great quality food. I think there is much better access to a variety of foods, of suitably high quality, and the variety of cuisines at restaurants is laughably incomparable. The prices are definitely higher, but the median income in SF is significantly higher, so I think it may still be a smaller % of salary for most people.
For some reason people associate fast food and junk as "American" and then extrapolate that as what typical American diet is. Maybe there are parts of the US that are much poorer and with worse access to food distribution, but I'd assume that rural and impoverished Europe is the same.
In the current age everyone can eat everything everywhere, apparently there are even people who fly their bread everyday from France to New York. So when we talk about food in some place, its usually about the general practices and not the possibilities.
For example the food in London is shitty even if you can find some of the best restaurants there. The problem with London is that you can't fit those restaurants into your daily routine, the default is a sad meal deal from Tesco or something.
Yes and unlike London, the default in many parts of America are great.