If your root cause is cross team, then you wind up having to make some implicit assumptions on what the other team could have done. Is akin to ending with "because the gods got angry." Not really actionable.

This is a classic "limit the scope of the feature." You want the document to be written and constrained to someone that is in a position to impact everything they talk about. If you think there was something more holistic, push for that, as well.

Note you can discuss what other teams are doing. But do that in a way that is strictly factual. And then ask why that led your team to the failure that your team owns.