Uhh, they already are on the STARNet P25 system across 98% of the commonwealth at this point. It takes time to build out all of the sites and install/program thousands of new radios, cut over to a completely different system, etc. Considering the scope of the migration from OpenSky to ASTRO 25, they have made remarkable progress, and are on schedule to decommission the OpenSky system later this year.
Besides, what does it even matter? PSP is 100% secure, so it's not as if you can listen, no matter what system they're using. 🤦♂️