Because he had, several years ago, gotten to the point where most of the major U.S. banks were no longer willing to keep lending him money. Deutsche Bank was a notable exception, and they’ve since been under investigation for shady dealings. (Note: the article below is from 2017.)
To borrow money, Trump has had to turn to smaller and less conventional sources of capital, such as Ladder Capital Finance, a New York real estate investment trust that holds mortgages on several Trump properties. Ladder doesn’t keep the mortgages it issues and instead packages them into securities and resells them to other financial institutions. It therefore has somewhat more freedom to take risks with its customers than more heavily regulated banks.
More troubling is Trump’s relationship with his other major lender, Deutsche Bank Trust Company Americas, a subsidiary of the giant German bank, says Eisen of the Brookings Institution.
Deutsche Bank Trust Company Americas is in talks with the federal government over various financial irregularities and faces big potential fines over its handling of mortgage-backed securities. Like other big banks, it will be affected by Trump’s vow to overhaul bank regulations.
"Here you have one of the world’s largest financial institutions, Mr. Trump’s principal lender, whom he owes many, many millions of dollars to, that creates a conflict that cuts across Mr. Trump’s job as president, " Eisen says.