All of his pardons so far have been political, that is to loyalists or those who were willing to pay him a bribe campaign contributions. If he were to make pardons of mercy, the public would suspect they were political merely based on the precedent he's already set.

However, I can't even imagine Trump willing to make mercy pardons at all. Trump really is that stuck in a transactional mindset, and cannot do a positive thing even as a publicity stunt. Every step he takes has to enrich him.