Obama barely got the ACA through the Court, and that was by a breath. He would not give up the opportunity to make sure it's never that hard again.
That's bad, because it will perpetuate party politics. No matter how much people dislike the candidate nominated by their party, they'll think they've got no recourse but to vote for him/her lest they lose the Court.
All the Republicans I know who say they'll vote for Clinton before they'd vote for Trump - and there are plenty of those - won't follow through. The chance we might have had for an olive branch, reaching out of the viper pit of party politics, is now gone.