According to the GSMA last year phone theft (which arguably has much more part serialization and anti-theft measures implemented) has been a steady 1% of smart phone users worldwide. It does not seem these attempts to lock down systems are successful in reducing theft. https://www.gsma.com/solutions-and-impact/industry-services/...

However I wonder if they have had an impact on data and financial theft. Which things like part serialization wouldn't affect but system security measures would.

In the early days, iPhones being both extremely popular and expensive made them pretty big theft targets and Apple was getting pressure from the various state governments to "do something" about the increases in phone theft. At least according to NY and CA, the activation lock alone in iOS7 caused double digit drops in the iPhone theft rates: https://appleinsider.com/articles/14/06/20/police-say-ios-7-...

Alternatively, without these measures phone theft might be a lot more than 1% of users. People get killed for less than a smartphone costs.

It’s a dynamic system. The number staying the same doesn’t tell you anything about causality or the counterfactual.

I suspect the majority of phone thieves don't care about the previous owner's data, they just want it wiped so it can be sold to someone else.