re: With Biden most likely not running for office, what is their reason for holding back?

Biden won't be the Dem candidate. I've said it for months. The reason for holding back could be that Biden isn't willing to step back, forcing the Dems to maneuver around him. Also, could be they want little time as possible for Newsome to be on the national stage.
It will be sold off as Joes health problems or something will happen along those lines.