The difference is what Trump did after it was discovered he had the documents. Unlike the Biden, Clinton, and Bush cases, Trump dragged his heels for over a year after the Archives had requested the return of the documents, resulting in the government's having to get a search warrant. Even after the warrant was executed he is accused of hiding documents and instructing his attorneys to falsely claim that everything had been turned over. In other words, he willfully obstructed the return of the documents and the investigation into their return.
It's notable that the indictment doesn't charge him with the illegal retention of any of the documents he turned over, suggesting that if he had turned over all of the documents he probably wouldn't have been charged with anything. As others have pointed out, Trump is his own worst enemy.
If Trump really thought the documents were his personal records he could have gone to court and had the matter judicially determined. Instead, he concealed, lied, and caused others to lie. Of course, it's much more likely that he viewed the documents, while clearly Presidential Records under the PRA, as his personal trophies that his massive ego had convinced him he was entitled to keep and show others.
