All they do is regulate the flow of new money, they aren't responsible for tax codes that ensure a widening gap of wealth via the return on capital vs the return on labor.
https://en.wikipedia.org/wiki/Capital_in_the_Twenty-First_Ce...
https://en.wikipedia.org/wiki/Capital_in_the_Twenty-First_Ce...
They also implicitly affect asset prices which is probably one of the primary causes of wealth inequality.