Both can be true at the same time. Yes, most of the news media is ideologically liberal especially on cultural and social issues, and I'm sure they prefer to report things that support their bias. However, that doesn't have to keep them from fairly reporting the news. Plenty have done it over the years. It reminds me of Tim Russert. He worked for Mario Cuomo. I'm sure he was a pretty liberal guy, but on Meet the Press, he was pretty fair.
Nevertheless, news is a business first. They get paid according to how many people watch or read them. What I suspect they're learning is that the market for fair and accurate reporting of political news is pretty weak. Most people who are going to consistently watch have strong opinions, and they aren't really watching to learn what's going on. They're watching to have their opinions corroborated and reinforced and their egos stroked.
If you are a coastal liberal, CNN and MSNBC will cater to you. They'll tell you how immoral and stupid Republicans and "middle Americans" are and how righteous and erudite coastal liberals are. Obviously, Fox News and OAN largely do the reverse. Might these outlets occasionally give you a brief and obligatory viewing of the opposition's view? Yes, because they don't want to be accused of being raw partisans. However, they'll dismantle their arguments (both fairly and unfairly) and largely leave the preferred side unscrutinized. Both sides win. The networks make money, and their viewers feel good about themselves. But of course, the culture gets dumber and more toxic.