If they knew that some significant percentage were not locked they would be worth stealing again, and if it’s locked they just throw it in a dumpster.
The fact that your phone is locked protects everyone else as well.
Do you even believe this? I haven't seen any examples of thieves saying "stick em up! Oh, iPhone? Have a nice day"
Easy counterexample:
> an entire wall of iPhones (approximately 436) were gone
https://www.usatoday.com/story/news/nation/2023/04/07/apple-...
Another easy example:
> In the UK in 2016, there were almost half a million mobile phones stolen [...] _most of them iPhones_
https://www.trustonic.com/opinion/smartphone-crime-turning-t...
> In New York City, robberies (which typically involve a threat of violence) of Apple products dropped 19 percent and grand larcenies of Apple products dropped 29 percent in the first five months of 2014, compared with the same time period from 2013, according to a report from the New York attorney general’s office, which included data from the New York City Police Department. By comparison, thefts of Samsung products increased 51 percent in the first five months of 2014, compared with the same period a year ago, the report said.
https://archive.nytimes.com/bits.blogs.nytimes.com/2014/06/1...
* iPhones are very commonly stolen
* Android devices introduced a similar kill switch in 2014
> Samsung introduced to kill switch for its Galaxy S5 in April, so it will be sometime until its effects can be evaluated