If I'm not mistaken, baggage theft from gate-checked cabin bags has been rising at a faster clip than theft from counter-checked-in bags in the US. And I assume that gate-checked cabin bags are less likely to be locked than counter-checked-in bags, just about everywhere.

Not sure what all to make of the above myself, but ease of access to the bag without leaving as obvious a trace of utilizing the easy access to the bag is the kind of opportunity a thief or other miscreant would probably love more than more challenging access opportunities. Time is of the essence, generally even for thieves who don't want to get caught.

A high-end unlocked gate-checked cabin bag is frequently going to have more valuable contents than the same kind of locked bag checked in at the check-in counter? I would expect so, and that would make the former (unlocked high end gate-checked bag) more lucrative of a target than the latter (locked checked luggage) for thieves and other miscreants.