I think the leading guesses are perceptions about his age, the economy, and his effectiveness. Biden’s favorability is similar to Trump’s at the same point in his presidency, which was, itself, one of the lowest in modern history.

It’s nonsensical but I’m not surprised. Even here on Lemmy, some people refuse to give Biden credit for anything. Cynicism is rampant on the left. I think those who are paying attention see that Biden is governing pretty progressively. Sanders recently said that, “I think he is a much more progressive president than he was a United States senator.”