"The wealthy" generally structure their income to avoid it being "income", or hide it in jurisdictions the US can't see, or any of dozens to hundreds of other tricks to make sure they don't pay anything resembling their share.

This is a game as old as the US income tax itself; the 16th Amendment wasn't passed to legalize income taxes (they were already legal), but to make sure Congress could tax income "from whatever source derived", since wealthy people were restructuring their income streams to try to avoid taxation.

They still do that today.