After the 2008 financial crisis, legislations like the Volcker Rules to inhibit big banks from behaving like hedge funds. They are no longer allowed to engage in any forms of trading or financial innovation which leads to excessive multiplying of money supply leading and excessive leveraging within the banking systems.
Their income is thus restricted to investment banking commissions and net interest incomes.
Related references
Long-Sought Volcker Rule Revisions Land on a Changed Wall Street