"Liberals" didn't...otherwise they would of watched the shows. Fox News is popular because it's insanely popular with conservatives.
5 facts about Fox News | Pew Research Center
60% of Fox news watchers call themselves conservative and 23% moderate with 10% Liberal.
CNN is 32% conservative, 30% moderate, and 30% liberal)
MSNBC is (32% conservative, 23% moderate, 36% liberal).
Personally since the poll depends on self identification I would bet that a lot of those moderates lean heavily conservative for Fox news and lean heavily liberal for MSNBC, or Typically Republican voters or Democratic voters.
I just don't think Liberals like the format. 27 million unique listeners tune into at least one NPR show a week. That's why I think NPR is more representative of what Liberals want in a news show.