The financial sytem in a capitalist economy's job is to allocate capital. This is a tough job - figuring out which borrowers are credit worthy, which inventions deserve to be funded and brought to market, which companies deserve to go public, and once public, the financial system keeps tabs on all of them in order to provide capital to those that continue doing well, while it removes support from those that do poorly. It also provides insurance so that people and business can operate with a known cost in a world of risk.
For these services, the financial system gets paid. How much? Well if you look at the chart below, you will see that its paycheck has grown substantially over time. From a basic level of 1.5% the skim has increased to over 5% where it is today. That skim has increased directly as the total level of debt in the US economy has increased. Higher debt = more money for the finance guys.