I think evidence was coming forward implicating Joe was a co-conspirator in his business tax evasion. Hunter pleads guilty….no trial. Joe pardons Hunter. Then he hands power to Kamala.
There is the matter of the other family members being involved in the family business.
He can't guarantee they won't have charges brought against them in revenge by his fellow Dem playmates when he is gone.
There is no honor amongst thieves, despite the famous quote.