Why the conventional path closes
A conventional mortgage application is constructed around a Social Security number and the credit file attached to it. Without one there is no score to pull, no trade lines to review, and the automated process has nowhere to go. The decline isn’t a judgment about the borrower, the form has no field for them.
Meanwhile a home-country bank generally won’t lend against property in another country at all. So a buyer with substantial documented means gets told no from both directions.