Conjectures about shat might have happened are just that. Your examples are appreciated and instructive (much more for Republicans).
The Democrats have no success in replacing their POTUS candidate. None. What makes them think replacing one now will generate s different outcome? It boggles what little is left of my mind that the Democratic Party thinks replacing Biden instead of working harder will generate a victory for them.
Replacing the candidate this late is a risky gambit, sure.
But staying with Biden is at least as risky. And the deficiencies he has shown in the debate and in the interviews, as well as frailty that was for example demonstrated in this clip will not get better, as he is not getting any younger.
So changing the candidate, as risky as that is, is most likely the right move here. Your argument ignores the risk of sticking with Biden. What if he performs even worse in the second debate? Or falls Giuliani-style?