Nobody getting to vote for her is a sore point for the left base. Biden didn't all of a sudden deteriorate this summer, his handlers have known he was out the door by 2022, but there was zero attempts to challenge him. The plan was to always let him unexpectedly flounder in the first debate and switch him out with the appointed new face as late as possible. Kamala's policy page is still just a donation portal, she could be a cardboard cutout and they would run her to influence her privately selected cabinet positions.