Because that's exactly the point. Policies transcend parties. Biden's inept and shouldn't be in office, but he is the result of a need to get the global embarrassment that was Trump out of office, and the left trying to go as "moderate" as possible to appeal to centrists who didn't like Sanders.
We all need to agree to zero voter turnout at the next election, so we can break the system and force a new approach. But even that wouldn't work, because some left/right dumbass would put their ballot in just so they could say "I did it, I did it!"