The excerpt adarza commented likely explains it somewhat. Ships made shorter by cutting a section of the middle out & rejoining the ends. They probably both had the same modification around the same time, so reached a point of similar wear and (literal) tear at the same time. I’ll bet they forgot about their history and neglected to perform the more thorough integrity checks they required because of it.

To be fair, they’re not the only ones… *cough*Boeing*cough*