By decoupling the user identity from a permanent, globally unique IMSI, we make IMSI catcher / Stingray attacks less "useful" as the IMSI is changing and isn't

By decoupling the user identity from a permanent, globally unique IMSI, we make IMSI catcher / Stingray attacks less "useful" as the IMSI is changing and isn't tied to the user. They can attack your IMSI, but it won't be tied to you and it is ephemeral.