If you read the article it explains why the fact that it is an ordinary failure is a bad thing. Ordinary failures (like some one not installing some bolts) are not supposed to happen in high reliability systems like passenger aircraft. Failures tend to come through “extraordinary” failures where multiple factors line up in an over looked way in order to create an unexpected failure mode.
A 10 year old could tell you not installing safety bolts where they are supposed to be would make things dangerous. The fact that that is how a potentially lethal failure happened is damming.