Why are Japanese cars considered to be more reliable than US or European cars?

It's definitely true in the States. Due in part to import costs, we don't get many of the bare bones reliable models from pretty much anyone but Volkswagen. Other European brands either don't manufacture in the States, or only manufacture a small range here. For example, Mercedes-Benz and BMW pretty much only manufacture SUVs here because we can't get over huge ass cars, so it makes more sense to make those here since we buy so many. But our economy class market is too competitive for the good cheap Euro stuff. Additionally, Americans automatically assign European brands a level of prestige, which they want to maintain, so we get the fancy over-engineered stuff that costs a lot to maintain and fix.