This is anecdotal but it gets me thinking. Sometimes in the late 90s I stopped putting locks on my luggage. Locks were once or twice removed previously - and once the customs put a note saying they had done it. I was travelling to Europe, the east of Africa and various Caribbean countries. Nothing was stolen - but the key thing was me not storing anything too expensive in there. Generally all my expensive objects are delicate and will be transferred in my hand luggage.

Perhaps it's safety in numbers. Perhaps it's a kind of camouflage and not signalling anything of worth. Perhaps it's because the level of risk of theft is incredibly low.