The American people, inclusive of his Democratic base, did not want him to run again. He had stated in 2020 he was going to be transitional. Then he let his circle of advisors, including his wife and his son, commit elder abuse. And those people are hanging onto power until Jan 20, 2025. It's quite telling, however, that neither Obama, nor Pelosi, nor Schumer, nor Jeffries have committed to Harris.

It's quite clear that vast sectors of the media and his advisors and his administration have been hiding the true extent of his illness of his frailty and his possible neurological condition from the American people.

As for why Harris is not going to finish Biden's term? For the same reason that she will lose in November and that she came in 6th and didn't even make it to Iowa in 2020. Biden's administration is going to hold onto power for as long as they can.