Key in short sales is whether the lender kept the loan, sold the loan "whole", or sold "slices" of the loan in a securitization.

If there is an identifiable "lender" who owns the entire loan (whether the original lender or someone they sold it to), they will likely agree to a short sale. If the loan was packaged and sold as a securitization, then there are 100+ owners and the documents likely prohibit the servicer (the person who answers the phone when you call) from agreeing to a short sale. No practical way to get the 100+ owners together and say "out of the 500 loans you bought as part of a package, we would like you to agree to a short sale on one of them".

This is part of what makes the mortgage mess so hard to resolve. Many loans were carved up and sold in pieces, making it impossible to renegotiate the deal on any one loan. On the other hand, judges are starting to make the securitization buyers produce original signed notes and mortgages if they want to foreclose on a house. Often no one knows where those documents are stored. So the lender cannot foreclose even if the borrower stops making payments. Borrower gets to keep living in the house despite not paying the mortgage. So it is serendipity whether you are better or worse off if your loan was securitized. Drives people nuts. No consistency.

Hope you find some peace soon.