Another variation on 2x is to listen to 2 different people at 2x on the same topic can convey concepts better than listening to only 1 at 1x. Different speakers use different vocabulary, different analogies, etc.
As for listening to the same presentation twice at 2x, one reason it works better is that most narratives or lectures do not provide a "mental map" or "scaffolding" to hang all the sentences on. So the 1st pass feels like it's a bit random and incoherent but it lets listeners mentally build an outline structure in their head, and then the 2nd pass makes it easier to link the sentences to that structure and it feels more coherent.
If speakers did a better job of explicitly providing that outline structure and constantly referring back to it during the narration so listeners don't get lost, the 2nd pass wouldn't be as necessary.