[dmitrygr]

NTSB's M.O. has always been that there is never just one cause. A human mistake that costs lives is never that simple. There is a system that trained the person, a set of incentives that put the person into that place, a set of safeguards that should have existed to prevent the mistake from causing life loss, and a regulatory framework to occasionally verify all of the above. I would expect that "the controller made a mistake" would be ~one paragraph in a 100-page report.

[wolrah]

Exactly. In the field of accident analysis and prevention the "swiss cheese model"[1] is very popular for this reason. It acknowledges that every layer of the system will have holes, and that ideally every layer when stacked up provides complete coverage. If something bad happens that means that holes every layer had to have aligned and the whole stack bears some responsibility for the outcome.

1: https://en.wikipedia.org/wiki/Swiss_cheese_model