Note the paragraph below. Apparently NSM wouldn't accept the liability terms, which led to their dropping out:
Before completing the purchase, the winning bidder must overcome objections from ResCap customers, including its two biggest, Fannie Mae and Freddie Mac. The government-controlled companies have demanded in court filings that the winner take on the legal liability that ResCap currently faces for loans it originated.
ResCap’s $2.1 billion of 9.625 percent, third-lien securities, which represent almost two-thirds of its outstanding bonds and fell to as low as 57 cents on the dollar last year, have traded above face value for a month. They rose 1.25 cents to 104 cents today, according to Trace, the bond-price reporting system of the Financial Industry Regulatory Authority.
Nationstar’s $2.3 billion stalking horse bid for the right to service mortgages owned by Fannie Mae, Freddie Mac and others, was based on not accepting any potential legal liabilities for the loans, according to court documents
Overcomming "objections from ResCap customers" could take a long time and cost a lot of money -- sure sounds like a deal breaker to me. BAC, for example, is looking at another $1 billion law suit. Small wonder why NSM declined to up the bid further. There will be plenty of other opportunities which likely have better bottom-line prospects. Last I heard, Citi, BAC and JPM are looking to unwind their mortgage servicing.