Wide gauge isn't used as a "catch all" when the cause can't be found. It is quite easy to determine if wide gauge caused a derailment by careful examination of the track to determine
position of spikes in ties, prior tie scuffing by tie plates, wheel drop off points, rail
head scuffing, overall tie condition, bolt shear off points, rail roll over, just to name a few conditons to look at. (If the investigators don't look closely at wheel condition, sharp flanges and chipped wheels can can cause people to make a wide gauge determination.)
Wide gauge issues occure more frequently under spring thaw conditions where the frost leaving the ground impacts roadbed stability due to uneven thawing, excessive moisture, tie saturation and such----things that later stabilize once frost has completely left the roadbed and moisture distributes more evenly or things simply dry out. The transition from frozen to thawed is the time period where most weak spots in the track structure pop up. (Same is true for roads, spring is pothole season for similar reasons.)