When banks began to scale back financing for energy companies earlier this year amid the slump in oil prices, some of Wall Street’s savviest asset managers sought to capitalize by lending at high rates. That didn’t work out so well, as crude continued to plunge and lenders were stuck with losing positions. Now, banks are again contemplating credit cuts. But this time hedge funds and private-equity firms are showing more reluctance to step in. “Those so-called lenders of last resort are not out there this time around,” said John Castellano, a managing director at the consulting firm AlixPartners LLP who...