Why are the rich called "filthy"?

A jelly recently made a comment about “the filthy rich”. The filthy rich?

It is obviously designed to be a prejudicial adjective.

In fact, most of the really filthy people I have ever seen were poor.

Somehow I don’t think it would be nice to call them the” filthy poor”

But it is regarded as perfectly OK to insult and show disdain for the rich. Especially on this site. People call the US the richest country on earth (as if a country is a thing that can be rich). But if that is the case, is the US thus the filthiest country on earth?

Why not call them the beautiful rich, or the glittering rich. The industrious rich? The influential rich. Even the lonely rich if you want. But filthy?
Why this need to show disdain for the people who have accumulated wealth?

It clearly encourages destructive emotions like envy and jealousy. How can any social structure benefit by deliberately pandering to the lesser angels of our nature? And yet, even our president does it.

Just seems sort of petty to me.