I agree that fine-grained assignment of blame may not be that useful, but that doesn't mean that finding out where things went wrong is useless.

Maybe companies always focus on profits over safety; in that case, maybe nuclear reactors should be state-owned or not exist at all. Maybe the governmental oversight failed; maybe anyone should be allowed to inspect the reactor, or the IAEA should be funded to do regular inspections. Maybe one operator did something wrong; maybe hiring practices should be revised, or maybe any important decision should be signed-off by two senior engineers.