There's different aspects of the case, and you can't make one blanket statement.
When it comes to his belief that he could possess "documents", that's referring specifically to the diaries he had. Hur noted that Reagan kept diaries with classified information. This came up in litigation when the DoJ said that the diaries were classified but also personal property. Therefore, Biden had reason to belief he could keep diaries with classified information in them.
When it comes to his memory, there was one comment Biden made about "finding the classified stuff", however it's unclear what he's referring to and the defense would be that he did find classified information and forgot about it later.
Compare that to the case against Donald Trump where he very clearly committed numerous acts that violated the law, including obstruction of justice, witness tampering and attempting to destroy evidence. What kind of person would vote for such a criminal?
Because when you vote for a criminal who doesn't give a shit about the law, you run into situations like this where Trump thinks he can give himself $230 million taxpayer dollars as if that isn't insanely corrupt.