All of these pundits are especially conservative (small c) with their evaluations after 2016, and they still think incumbents have the upper hand, despite so many going down in general elections in 2018. 538 is the same way, and even think Trump’s incumbency gives him an advantage, despite Trump’s apparent attempt to squander it at every turn.
On the other hand Cook has written that the presidential election is fully baked in Biden’s favor. I agree, and as pollsters start polling while people have started to early vote, and it favors Ds by 2-1, their “likely” voter evals will move a critical point or two in favor of Ds and, perhaps, demoralize R voters and entice swing voters to pick the likely winner. That’s how you can generate a rout like in 1980.