One reason we don't know more about why Boeing aircraft suffered fuselage skin cracking can be tied to regulatory decisions made by the FAA. A Southwest Airlines 737-300 suffered a crack in its fuselage on April 1, and an American Airlines 757-200 suffered a tear in its skin last year. Both incidents led to the discovery of symptoms that could lead to similar problems on other jets. In the case of the 737, rivet work was questioned. In the case of the 757 the NTSB determined that the aircraft's skin was of nonconforming thickness -- it was thinner than it was supposed to be. But Boeing's records of how those and other affected planes were built and inspected were missing ... as directed by the FAA.
This is a companion discussion topic for the original entry at https://www.avweb.com/news/ntsb-identifies-record-keeping-loophole