Where the belief comes from
It comes from a real experience. Someone walks into a retail bank, asks about a mortgage, and is told no, because the underwriting that bank runs starts with a US credit score and a Social Security number, and the applicant has neither. That is a true answer about that lender. It gets heard as a true answer about the country.
The gap is that a bank branch and a wholesale lending channel are not the same market. A product that does not exist on one desk can be routine on another.