Once again, banks are struggling to expand their loan books. But they have an ace up their sleeve: lending to nonbank lenders.

Across several large, global, national and regional banks that have reported earnings so far, a common pattern is tepid loan growth. The year-over-year average loan growth at eight commercial banks—ranging in size from JPMorgan Chase to First Horizon—rounds to zero. Many are still shrinking their commercial real-estate loan books.