In an age where printed periodicals were delivered by subscription, the subscriber information was available (and yes, often tracked by local and federal law enforcement), but not the specifics of what articles were read.
Today, with Web-based document delivery and Javascript instrumentation, the specifics of who reads what articles, time on page, sections read, interactions, shares, and more, are available not just to the publishere but advertisers, any entities hacking into or accessing their systems, app developers, and more.
And, yes, law enforcement, whether under warrant, subpoena, or ... other methods.