Honestly, I don't think it's any more complex than the fact that he's burdened with an serious sociopathic personality order that trumps common sense, restraint and good judgement.
(excuse the pun)
Personality wise, he's not cut out for the espionage life.
He's attention-seeking, flashy, loud, crude and desperate to remain hi-profile.
He's anxious, angry, mendacious, paranoid, disruptive, explosive, distractable.
He craves headlines and reactions - good or bad.
He needs the spotlight like the rest of us need air.
He's projects his own bad behavior in advance.
He is untrustworthy - clearly not going to keep your confidence, your state secret, your crimes, or anyone else's to himself.
Here's my theory: I think a stunned, hurt, narcisisstic-raging lame duck forgot to pack his piles of papers strewn throughout the WH and residence - b/c he was very busy raging and gaslighting and deluding and insurrecting w/ Rudi and the gang.
More likely, in last minute moving chaos, he ordered WH staff to box "his papers" strewn around the white house - orders to "just pack it all and bring it to MAL". (See Melania's texts - she's annoyed with his paper boxes - in the indictment - she knew they weren't personal papers that needed to get to MAL.)
Perhaps he thought he'd have time at MAL to (pick one or two): read and cull, lick wounds, boast, reminisce, refresh his memory for a book he'd write, finish reading things he'd set aside, plan his presidential library (ha ha ha ha okay, just kidding). Perhaps he was sure in the boxes somewhere were docs he could use for insurance/protection/revenge/blackmail/threats - ya never know - against friends or enemies, for congress or the courts.
When he was asked/told/ordered to return these papers b/c they were NOT his ... well. What ensued is just classic narcissistic entitlement disease. They. Are. Mine. How. Dare. You. My. Presidency. Has. Not. Ended.
So ... did he select or intend that these docs for his next grift a.k.a. espionage-for-retirement-dollars? IMO - Nah.
He already had a great grift going - the re-election campaign grift.
He's far too lazy to start anew.
He's far too loud to spy.
(I don't mean to minimize the real risks and endangerment of his sociopathic behavior, poor judgement, willingness to share state secrets for self-aggrandizement or keeping blackmail handy. But, I imagine the Feds investigated/eliminated the spy-for-$$$ theory prior to charging.)
JMHO