So, for me, these have been the two questions:
1. Was Jan 6 an insurrection or rebellion?
Many will say they believe it was. Many will say they believe it was a giant protest. Neither Insurrection nor rebellion are defined in federal law.
2. If J6 was an insurrection or rebellion, did the President incite, set on foot, assist, or engage... or give aid or comfort thereto?
Whatever it was, some will say they believe he incited it. Some will say he did not. It does not appear that he "set on foot". He didn't appear to assist or engage. And I don't recall any evidence of aid or comfort to those who were involved (I may just not be aware.)
And the uncertainty of what it was and his involvement is why media outlets say 'believe'. We all saw what we saw, but since we've never seen it before, it is subjective. Media corporations can't say it was it was a thing (yet). Saying it was a thing, saying he incited it, and then having a Court rule otherwise would likely shut down a network. That libel / slander lawsuit would be settled for billions.