criminal or civil liability.
Half the people are dead so will never be able to be tried in court, and similarly the organisations that enabled this to go on for so long without being discovered are very unlikely ever to face a criminal prosecution for it by the CPS (the CPS being one of those organisations that could itself be held liable potentially).
If the inquiry were able to assign liability to those organisations, then the victims would at least be in a position to claim compensation from them. Without this, it would be left to the victims themselves to fund a civil legal action that would actually have to do all the investigation and prove that liability themselves in court, against the likes of the MET. That's a very unequal fight.
eta - this inquiry also had no legal power to compel witnesses to attend AFAIK, whereas for example, the investigation into abuse within families under the children's commissioner's authority had the threat of 6 month jail terms and large fines for anyone who refused to appear before them.
That is a massive difference, and as there was already the precedent set for such an inquiry to be held in that way under the auspices of the children's commissioner, it begs the question as to why this route wasn't followed this time if they wanted the inquiry to really be taken seriously.
Whether a system is inquisitorial or adversarial is largely irrelevant as to liability.
Liability is a question of a substantive test, whereas the route you use to determine liability is a matter of procedure, not substance.
Furthermore, you seem to assume that the matter is proven, or, at the very least, almost certainly likely to be proven, which is, at best, unclear.
But the really important point on inquisitorial v adversarial is that, without proper oversight or appropriate checks and balances, the inquisitorial system lends itself to mission creep far more readily than the adversarial system does, especially when those under investigation are dead and cannot defend themselves in personam.
My opinon is that inquiries of the kind favoured by the current government undermine the rule of law.
They are sops that quell public opinion or address special interest groups in a manner that is of little utility and encourage the peculiar form of litigation that they generate -
i.e. a lot of lawyers getting wealthy by addressing an investigation with such a massively wide and ill-defined scope as to be essentially meaningless in its conclusions (while being unable to act on them also!).
Distraction from more important, present issues very well done...