1. It would destroy Pence’s political career, since he is probably the front-runner to replace Biden in 2024.
2. Accepting a pardon is an admission of guilt.
3. It wouldn’t protect Trump from factitious charges in states courts pertaining to any economic interests and given the apparently censorship of politically incorrect news (and the control the major internet companies exercise), Trump is at a major disadvantage
4. Politically the smartest thing Biden could do would be to order the Justice Department to refrain from any political prosecutions (allowed, since Common law prosecutors always have the discretion not to proceed).
5. Especially given the media monopoly on the left, as well as the “cancel culture”, is that the Trump base will increasingly regard the government as other than democratic and not governed by rule of law. A Biden pardon would totally change the climate politically, though that is unlikely.