I was invited to a research institute in Russia and was warned by the hosts that theft from checked baggage was very common in Russia. I was advised to carry everything with me onboard the aircraft. It's not that there are more thieves in other countries than in the US, but even items that cost only a few dollars in the US and may not be worth stealing, may be of considerable interest and value to thieves in poorer countries, hence increasing incidence of theft. Secondly, theft is not the only way one can lose things. Even locked bags sometimes mysteriously open due to the rough handling. I have lost maintaintance medicines from my briefcase during random check at the gate on my way to Vienna. I don't think they were stolen. The checkers were just sloppy. But the incidences of theft/loss are likely to be far higher when millions of bags are unlocked.
However much the Govt may want us to leave our bags unlocked, it is not right.