Used hiking boots are hardly most people's idea of 'valuables', nor do most people think they will be attractive to thieves. BTW.. you don't wear plastic mountaineering boots on the plane or to walk around (not as bad as ski boots, but close) and their carry-ons were jammed with what were presumably more attractive targets: electronics and dive gear, prescription dive mask, etc.

The point is that just because something works for you and makes sense for your personal style of travel, don't assume it works for everyone else. It's quite possible that these folks would have still had their gear if they'd locked their bags. I did and my gear arrived intact. Metal zips, a remarkably shabby bag and a lock must have been just enough deterrent for the baggage handlers to move on to a more easily accessed bag.