Say what you want about Biden, but as a politician he should've been experienced enough never to let it come this far. The same goes for the Democratic Party. Even if Biden was fit as a fiddle, his presidency would've ended after 8 years at the max. In other words, sooner or later they'd have needed a successor. Why wasn't a successor being groomed these past four years? I mean, surely you can't say Harris was being rolled out as Biden's crown princess. Neither Biden nor the party gave her a high-profile role. It's just weirdly incompetent.
And why did Biden not go onto the campaign trail in 2019 saying he'd do one term and then pass the torch over to a younger generation? It would've made campaigning much easier for him, too, deflecting much of Trump's criticism about his age. After all, four years ago he wasn't in as bad a shape as he is now. Just out of curiosity @ all Americans around here: Do you think it would've hurt Biden (or any presidential candidate for that matter) to stand for the presidency with the caveat not to seek re-election after four years?
Everyone's blaming Jill Biden for forcing Joe to continue, but it seems to me that the actual culprits sit in the party itself. The potential successors seem unprepared to throw their hat into the ring at this point, so they'd rather keep Biden in as long as it keeps their intra-party rivals out.