Privacy advocates got access to Locate X, a phone tracking tool which multiple U.S. agencies have bought access to, and showed me and other journalists exactly what it was capable of. Tracking a phone from one state to another to an abortion clinic. Multiple places of worship. A school. Following a likely juror to a residence. And all of this tracking is possible without a warrant, and instead just a few clicks of a mouse.
Because a carrier’s data on you is not your person or belongings. The companies holding this data are selling access to it, so it’s not being searched, it’s being offered.
In other words, the same reason as why they don’t need a search warrant if there’s a breaking and the business across the street volunteers their security camera footage, even if you’re on that footage.
Courts have actually said that looking back at someone’s location data counts as a search and requires a warrant. There’s currently a lawsuit recently filed by the institute for justice aledging that the use of flock safety license plate readers is unconstitutional because it’s a warrantless search.