He’s definitely keeping his word on that. Clyburn had endorsed Biden’s campaign and has talked about his promise, often. I assume Clyburn is holding him to it. Though it appears defeating to limit his choices this way but I doubt it was without deep consideration.
My thoughts on his statement during his campaign was he will be making up for his Anita Hill snub (condescending remarks) allowing Thomas to be selected to the bench.
Logic? Isn’t it always a political ploy, gamesmanship, the need to be the guy who did it first - his Legacy?