Except there's no such thing as a hollow blue suit! Any alternative to Biden has to be a real live human being, probably with real live political aspirations of their own. That means they're going to want to win. Anybody who stands any chance of being anywhere remotely close to competitive also stands a chance of outright winning under better circumstances in four years.

You're asking an ambitious politician to take a real, serious risk of political suicide just to save face, and the reality is that no matter who your replacement is, polling better than Biden isn't a win condition. Winning the election in November is the only good outcome. All other outcomes are bad not only for the nation but also personally for whoever replaces Biden.

Sure, you can run a would-never-win-or-even-run-anyway candidate, but like I said: that's essentially conceding the election, and Biden can do that on his own.