I think a much more simple answer is that syndication has always been hush-hush because branding and brand trust is a key part of media marketing. Your local newspaper in the 90s had a ton of syndicated stories too but it was all published under your local paper's hometown moniker.
Moreso this (at the time) was literal school content on media literacy. High school english classes would _get newspapers_ in order to talk about the different types of articles and content.
That aside, I'm not sure the assertion about 90s papers is accurate. There was syndication, of course, but that was attributed. Let's say there were articles written by other people published under the names of local writers. That sounds theoretically possible, but something that'd be well known. Let's say there were articles attributed to the paper at large. I don't recall that.
> The average American reader didn’t necessarily notice the way syndicates and chains had come to dominate the news. Syndicates were careful to sell their material to only one newspaper per city. While syndicated features usually carried a small copyright symbol, the name that followed that symbol could be deliberately opaque. Readers wouldn’t automatically know that “King Features” denoted Hearst material, or that “NEA” indicated content from the Scripps chain. Local papers sometimes purposely disguised syndicated material. The Milwaukee Sentinel bought a comic strip from the New York World syndicate in 1918, for example, but retitled it “Somewhere in Milwaukee.” The same paper told readers to send in their letters for Dorothy Dix as though she could be reached in Milwaukee, and not in New York City, where she lived and sold her work to the Ledger syndicate.
https://www.smithsonianmag.com/history/how-syndicated-column...
Local newspapers didn't want to plainly advertise that a gigantic chunk of their content came from thousands of miles away. It undermines their value proposition.
Likewise, CNN probably likes that a huge chunk of featured content on their page is driving them revenue but doesn't look like a big ad to their audience.
