As I recall the few Democratic commentators who publicly said Biden should not run again were big progressives who didn't outright suggest a different candidate, they were just thinking/hoping pretty much any younger candidate would also be more progressive, but they had strongly supported Sanders running the previous two times in a row which does feel a little ironic. Sanders didn't make the kind of blunders but it is a weird situation where the biggest, most prominent politicians and those basically represesenting the poles re people Sanders', Biden's and Trump's ages.