IMO this should have been included in their threat model. The only way to exclude yourself from insider threats is if insiders cannot possibly become threats.
But then what if one of those essential people goes rogue or falls victim to a spear-phishing attack or family ransom etc. How do you mitigate that? Perhaps have a "two keys" to unlock protocol such that two separate team members are always required to unlock sensitive data and i.e. always supervised.
I don't know the solution, genuinely curious how this is solved in practice.