The rich invest in hard assets that produce income. Whether that's dividend from stocks, or rental income from commercial buildings. That recurring income is usually enough to service the loan.

And remember the ultra-rich themselves own the bank. Warren Buffet has huge multi-billion dollar positions in Goldman Sachs and Wells Fargo, in addition to owning the real-estate arm of Berkshire Hathaway itself. And the ones that don't own the banks, still get favorable personal treatment from banks in order to get their M&A or underwriting business.