This WSJ Article out today but I can't post the link yet, perhaps someone else can.
Inside U.S. Airlines' Decisions to Keep Flying the 737 MAX
Interesting quote from the article:
No problems had shown up, says Neil Raaz, American’s director of flight safety. “We just didn’t see the indications that told us our airplanes were unsafe, and frankly, we still haven’t,” says Mr. Raaz, who is also a Boeing 737 captain and has U.S. Navy and National Transportation Safety Board training in accident investigations.