"Joe Biden, did not want to admit his senescence. "
No, not just Joe. There were a lot of younger people who did not want to confess Joe biden's state because it would reduce their power and a lot of them were under 65.
True, but there were also many younger people who never wanted him to run in the first place. One of the major downsides of the two-party system is that the major parties maintain a duopoly of power, significantly stifling alternative movements (like the Sanders progressives) from making major inroads politically even though public support is widespread. This is a systemic flaw in American politics.
This is an intentional feature of modern American politics. It's not what the founding fathers intended, but if you think that gerrymandering, lobbying, and 2 party dominance don't benefit those who currently hold power in the US you're crazy.