See so many of these because of wrong size ball for hitch, unlubed and now corroded ball causing seizure and unscrewing of the ball. I have seen that twice.
Improperly torqued and no lock washer or enough to imbed the little balls on bottom of the ball into the mount. Lots of stress on that ball.
most people don't even think of cleaning them and replacing a corroded ball, or cleaning the hitch on the trailer and lubing the ball.
Then the screw down and little wing to hold the nut in place, not tightened because it is rusty etc
Some don't seem to think the chains necessary or know to cross the and make sure they won't come unhooked. On trailers with I bet half have a dead battery for the break away safety or is even hooked up.
When Retailers sell a ball mount or trailer, at least they could inform them and give them a booklet or something, if they would read it.