These stats are unfortunately not exclusive to America. It is also visible in other countries in Europe in the last 20/30 years. A lot of European countries copied the Anglo-American free market model based on trickle down economics, a policy even adopted by social democratic and centrist parties.
In theory, this concepts entails lower taxes for the rich and big companies, which would lead to more spending, more hiring of people in lower classes, higher wages, and consequently leads to higher welfare for everyone. And it worked, up to a point. Welfare has indeed increased in the first years of implementation of free market economics but slowly diminished in recent years.
In recent years, the rich and big companies have accumulated more power and influence than ever before. A lot of rich people have found judicial routes via expensive (international) law firms (e.g. Mossack Fonseca) to bank their money in a safe (tax) haven, without paying almost any dime in taxes. A luxury that average Joe or Jane cannot afford. Another thing is that big companies threaten governments by taking their production and workers elsewhere if they have to pay their fair share in taxes, like Shell (big oil concern) and Unilever (produces almost everything you can think of) in my country. Small grocers, blue collar workers, teachers & others are paying their fair share to help finance public transport, schools and hospitals, whereas most big corporations want to enjoy the fruits of their labours. Because of all this, it makes it pretty hard for a government to use enough taxpayer money to finance basic public needs.
And yet, despite the decrease in welfare here and in America for the ordinary folk, lots of people are still voting for politicians that protect this model.