It's a popularity contest among 150 academics. A group that has swung hard against Republicans recently.
But really regardless the current president shouldn't be on these. And not that it has come up before but current candidates probably shouldn't be on there either.
I think in 30 years we will see Biden's first term as much more politically successful than Trump's, and probably Trump's as more influential as a break from Reagan/Bush conservatism. Historians will weigh these two things against each other and I bet we see Biden well above Trump but we don't have enough information, it's too soon.