“Couldn’t someone go outside and close the door?”
No. Seatbelts Fasten light on.
I had a 1971 Gremlin that had a rusted out driver’s door latch and it finally wouldn’t shut tight and latch. We held it closed with rope for a while, an I finally fashioned a new locking post from a bolt and nuts inserted into the frame. Actually worked. We never took the car to 30,000 feet, though.