I've observed something similar with suitcase handling at airports, where they are thrown around and piled up like it's typically done with bags of rice for example.
The odd thing about this is that it can be much more work to handle things roughly.
One time I was waiting for a flight and watching the activity out the window, and the guy who was transferring bags from the little truck-train onto the ramp that slides them up into the airliner was throwing each bag into the air and onto the ramp.
It was clear that it would have taken much less effort to just set each bag onto the ramp - wouldn't even have to be gentle, just don't go the extra effort of throwing them in the air.
But I guess treating them gently wouldn't have offered the same satisfaction.
My favorite from checking guns a few times is that I notice that the only thing they don't toss is the guns (which are obvious because they're marked and padlocked unlike anything else). Guns are set aside, loaded last, unloaded first, and moved carefully. Everything else, tossed.
I thought the same until one day my checked gun turned up missing and the airline not care about it any more than any other lost luggage and it turned up about 3 hours later having been misrouted to different airlines luggage area.
Treating the bags gently takes more time and effort. For starters you don't know heavy the bag is, so first you have to figure that out, and you have to spend effort managing its downward trajectory. It's more wear on the joints and body to handle it carefully than to just throw each bag with good form.
I don't know what I'm talking about, so treat that with a grain of salt, but it's plausible.
