Someone keeps stealing, flying, fixing and returning this man's plane. But why?

From what I've been told by fixed wing pilots, flying a plane isn't really that hard. At least one baggage handler stole a commercial passenger aircraft recently and flew it out, including acrobatics.

Flying one in a safe manner and following all the rules can be pretty difficult however. For example there is an area near me that is from the air as boring as any other part of Texas. It's controlled airspace because it is the Bush Family Ranch. The secret service will investigate you if you fly over it.

Unless you're inside a place with special flight rules (like the Washington DC area), you can just fly your plane whenever you want and don't have to file a flight plan or tell anyone. Small airports often don't have ATC so all communications are on a single frequency that all pilots trying to take off or land are tuned into. It's like being at a four way stop sign, there's "right of way" protocol to follow so you don't need to do much other than just announce your intentions to anyone that cares to hear them.

Really the only way to handle this is to put your plane in a locked hanger or chain it to the ground with a lock and then pay for whatever flight tracker that will alert you whenever a specific tail number is in the air. Follow it and then call whatever local police when it lands.

It depends on the airport! Some smaller airports (like Corona Municipal Airport where the story is based) - are untowered, meaning that there's no central ATC to chat with when taking off/landing - everyone announces what they're doing as they're doing it and there's a traffic pattern/flow that everyone follows to ensure there's no conflicts - it works surprisingly well.

In the US, you can get shockingly very far without having to chat with ATC.

Plenty of airports do not have controlled airspace. I've been to at least one where the local frequency was played on a loudspeaker on the ground so that people on the runway knew when a plane was coming in for a landing. The pilot still should communicate what they are doing, but they don't need approval to land.

Every time Douglas Adams' biscuit story is told, I laugh as hard as if I were hearing it for the first time.

Can we just not assume drugs or some other crime?

Edit: also this version of the biscuit story is missing the final extra flavor text! The version I read ended something like, “What I love about this tragedy is that there is another bloke who has been telling the exact same story about an insane person stealing their biscuits. Except his version does not end on the punchline.”