Political unity/ preventing a revolt. Presidents have a duty to ensure "domestic tranquility."
It was one of the reasons cited by Ford for pardoning Nixon, so there is precedent there.
Yeah, Harris should essentially tell Trump she'll pardon him if he agrees to fade quietly away. That won't necessarily stop the Maga nuts from two years of histrionics but without Trump leading the rallying cry maybe they'll lose steam.
God forbid trump lives long enough to run again as these clowns would nominate him all over. We need to move effing on.