At some point, the metadata is (user X talks to SaaS service Y), and then the trail goes private.
If ATT had really pushed back, the NSA would have been hard pressed to install and run tapping equipment. And that's on hardline voice, where CALEA obviously applies. But as far as I know ATT didn't really fight, once they were legally covered from liability.
The modern large scale cloud or social providers are younger companies, have fewer government ties, and (critically) have worldwide business.
I would automatically assume they all have data sharing agreements with the NSA, as a maximal threat assumption, but as a likely threat I expect it'd be a lot harder for the NSA to co-opt them.
I.e. why the NSA instead chose to tap Google's private fiber between their data centers
They're still pushing this stuff today, not surprisingly:
https://www.ctinsider.com/news/article/NSA-director-pushes-C...
> "WASHINGTON (AP) (Jan 12 2023) — A top U.S. intelligence official on Thursday urged Congress to renew sweeping powers granted to American spy agencies to surveil and examine communications, saying they were critical to stopping terrorism, cyberattacks and other threats."
"Other threats" such as what, populist movements unhappy with the increasingly feudalist-aristocratic nature of the United States and the gross corruption seen in Congress and the federal bureaucracy?