Since deregulation in the 1980s and 1990s, diversity in the financial services industry as it has gradually become monopolised.
From Mother Jones:
The nation’s 10 largest financial institutions hold 54 percent of our total financial assets; in 1990, they held 20 percent. In the meantime, the number of banks has dropped from more than 12,500 to about 8,000. Some major mergers and acquisitions over the past 20 years: