Over the past few months, the chief executive officers at two publicly traded mortgage firms and a private cooperative have departed, creating uncertainty in the market while underscoring what might seem obvious to some: It’s not easy running a mortgage business these days. CEOs heading for the exits – either on their own accord or via a management edict – include Jim Cutillo of Stonegate, Jeff McGuiness at the Lenders One Cooperative, and most recently Mark O’Brien, who headed nonbank lender/servicer Walter Investment Management Corp. And rounding out the “departure club” is...