It followed a long-established historical precedent.
Clinton pardoned his brother (https://en.wikipedia.org/wiki/Bill_Clinton_pardon_controvers...). The Bushes pardoned their Iran Contra cronies (https://en.wikipedia.org/wiki/Scooter_Libby_clemency_controv...). Trump pardoned his son-in-law's father (and now appointed him to be the French ambassador; https://www.cbsnews.com/news/trump-charles-kushner-nominatio...). Pardons have always garnered controversy.