Honestly, I think it's more of a practical matter. Even if they didn't have explicit pardon power, whoever's in charge of the executive has effective pardon powers by simply denying to carry out the orders of the court (see Jackson's behavior which lead to the trail of tears).
At least by making it official it's a lot more clear what's going on, and maybe they had hoped this would lead to electoral consequences for those who abused it?
I'd go to 2000 with a full report on how Bush stole the election so that the Gore campaign would be prepared to stop it.
If the 9/11 blank check had gone to Gore, then we might've jumped years ahead on the fight against climate change.