> you don't easily find, for example, yogurt without sugar added

I have a difficult time finding these, as well. The culture here (spoken as an American) is to avoid fats, which is why most products advertise "no fat" (yoghurt with no fat seems like a strange contradiction to me).

> in Asian restaurants (and even there, food is often sweetened)

This is also true from my experiences. Chinese restaurants add sugar due to believing that's part of the American palette. (For Chinese foods, there's also a distinction between "typical" and "authentic" styles, and most Americans are unaware of the latter.)