Household income is a stupid metric. In America, the top 20% of households contains TWICE as many PEOPLE as the bottom 20% of households. The top 20% of households contains FOUR times as many income earners as the bottom 20% of households. The top 20% of households contains THREE times as many children and HALF as many retirees as the bottom 20% of households.
So when someone says America has too many "poor" households. Consider that those poor households EXIST because they are WEALTHY enough to afford it!
Consider Italy. More households in the middle income share than America. Is that because Italy is an economic paradise? Or because of a strong, centralized bureaucracy capable of administering income distribution schemes? Maybe. But it could be the case that the old and young can not afford to establish their own households. So they continue to live with the working members of their family and enjoy the "benefit" of being a middle class household.
I don't mean to imply that America is perfect and that Italy is not. I only want to say that this chart is an awful way to represent data and is, in my opinion, intentionally misleading.