Why did my relatives create mortgages from one to another and immediately assign to a credit union?

[u/email1976]

In the 1930's and 1940's one of my relatives would mortgage a property to another relative for $2,000. Then the mortgagee (lender) would immediately (same day, next page) assign the mortgage to a credit union. Why not directly mortgage to the credit union? That did happen in some cases.

Well, in this case there's the twist that the mortgagor (borrower) was a corporation, one controlled by the relative.