Because Biden returned them that made it okay. Not that he wasn’t supposed to have them in the first place or not likely he took boxes and boxes out at once but suitcases and suitcase out a little at a time.
Because Trump exercised his right as a former president made them go through the law to get them they call that obstruction although he did t obstruct anything nor destroyed anything like Clinton’s and who knows with Biden because they probably don’t even know all he took is if lost somewhere or in someone else’s hands or were in Hunters who had access to them laying around everywhere.