I'm assuming that by structural limit they mean the limit beyond which the plane starts failing, not the point at which it fails. My understanding is that the most direct cause of the accident was flutter breaking the trim tab control rod. 20 year old bolts and reused nylon lock nuts make flutter more likely, deforming the airframe by flying beyond its structural limits can too.
I don't see how you could make this activity safer without spending more money on engineering and testing, or putting limits on what's supposed to be unlimited.