It increases the cost of overstepping in private messages, which would help prevent them. It decreases the likelihood of future private messages, since the offending contributor will no longer work together with other people from the project. It gives their targets a chance to continue working on the project without having to work together with that person. Why do you think it wouldn't help in any way?
And please don't be difficult by choice. As I wrote, it's not just about threats, but also about a host of other things (discrimination, sexually explicit/violent material, doxxing, personal insults, unwelcoming sexual attention, advocation for any of the beforementioned behavior, repeated harassment). Not everything is something you would approach the police over, but it's all stuff you don't want to be subject to because you contribute to an open source project.
And please don't be difficult by choice. As I wrote, it's not just about threats, but also about a host of other things (discrimination, sexually explicit/violent material, doxxing, personal insults, unwelcoming sexual attention, advocation for any of the beforementioned behavior, repeated harassment). Not everything is something you would approach the police over, but it's all stuff you don't want to be subject to because you contribute to an open source project.