If I recall correctly, the aircraft manufacturer writes the maintenance guidelines.

This could be a Boeing issue, if it’s due to something that happened at the time the aircraft was built, or due to a foreseeable gap in the maintenance guidelines.

It could be a Delta issue, if they weren’t following the maintenance guidelines, or a maintenance contractor working for them wasn’t following them and they didn’t catch it.

It could also have been (very small but nonzero chance) the result of physical trauma to the plane that wasn’t foreseen, back in the 1990s when it was built, as something that might cause an issue of this magnitude. I haven’t yet seen any information on whether this particular aircraft has a history of hard landings or running over debris on the runway. Freak accidents do happen.

All of those have precedents in aviation history.