I'm following from the logic of 2 random accounts who called this result beforehand, this was (roughly) their reasoning:
Republicans chose terrible senate candidates, abortion was a massive issue that polls weren't picking up (and it could be seen in by-elections right after Dobbs, where polling completely missed the results), and finally, after gas prices cooled a bit, Biden's approval went up a decent amount.
One thing I was wrong about was that the Dem strategy to promote GOP Nazis in the primaries worked - apparently they are winning those seats. Again, these 2 random accounts called this beforehand as well.
e - it's genuinely fecking absurd that 2 college students called almost every bit of this better than the polls