I think Biden still believes that things can swing back in the midterms or next presidential election. I don’t think he realizes that this might have been the last election that was possible to win.

If he does something drastic, he’d probably hand even more popular support to the Republicans in general and to Trump in particular who would play victims as much as they could.

If he does nothing, it might be the end of democracy, not just in the US but in most of the world. But he will have “accepted defeat gracefully” and considering he won’t live to see the worst of it, I imagine that’s all that matters.