Here's a good example both of how hard it is to compete for all-News listeners -- in a major market -- with a note about syndicated all-News formats.
30 years ago, in 1995, AM 1260 in Los Angeles (having just changed hands less than two years previous) went all-News as KNNS using the then-new AP All-News Radio feed. To have full coverage of Southern California, they simulcast on 540 in Orange County and San Diego. On-air, AP branded it as "The News Station".
"K-News" was up against two stations that had already been competing for the News audience for close to 30 years ... KNX/1070 and KFWB/980 ... which, on top of everything else, came under common ownership when Group W bought CBS Radio the same year as "K-News" started. And even though they executed the format on-air very well, with frequent traffic updates and local inserts, it lasted less than two years ... by the beginning of 1997, they pulled the plug.
The AP format had a decent affiliate count, but that declined over time and they finally threw in the towel in 2005. The audio simulcast of CNN Headline News ended two years later, and its successor CNN Radio, as noted, ended five years after that.
KFWB edged its way out of the all-News format in 2009 by taking everything outside of morning and afternoon drive to Talk. Then CBS bought KCAL-TV/9 and KFWB went into a trust to satisfy ownership caps. Two years later, they went all-Sports, and two more years afterwards, were sold and went to the "Bollywood" music format that was also airing in San Jose and Seattle. Even that wasn't a huge success, it was sold again and went to a Regional Mexican format.
And this was in market #2!
Takeaways, all validating
@TheBigA's points: It's an expensive format to run, and every attempt at national all-News formats ultimately ended with the plug being pulled. NIS had the resources of NBC. "The News Station" was backed by the Associated Press. The CNN Headline News simulcast was essentially part of CNN itself, and its replacement was operated by Westwood One.
There are only about a dozen 24/7 all-News stations left. None are purely FM.