Struck by other smaller but high energy debris, faulty batteries that are still receiving charge from unshunted solar arrays, similar mechanical failures from a

Struck by other smaller but high energy debris, faulty batteries that are still receiving charge from unshunted solar arrays, similar mechanical failures from attitude control systems, unused propellant leaks or ruptures. There are a lot of things that can go wrong which is why we have the 25 year rule now.