The taking of the documents is the least important of the charges. In fact, they didn’t charge him with taking documents. They charged him under the espionage act where he hid defense secrets, obstructed, lied, and conspired, shared those secrets, after numerous attempts by the authorities to retrieve them. And that all took place in Florida. Had they charged him in DC it would have delayed* the trial. The venue was a calculated decision of time vs judge/jury pool.
There’s also a good chance he’ll be charged in NJ for separate crimes regarding those documents since some of them were moved there. Separate case though.