I'm visiting with the fam for the 4th. My grandparents keep CNN on 24/7.
CNN has been running "Biden should step down" as their main lead, all week. Every show has at least one segment on it.
They're saying stuff like "70% of democrat voters think he is not fit" or something like that (dunno what their polling data and methodology are though.)
I expect that these 24/7 news networks can apply a lot of pressure to drive a story like this.
Edit: I may have misquoted those polls. Which I think shows how bad CNN's reporting is. They just said something very different came out of a Reuter's poll.