There are some conglomerates that own large numbers of media outlets. For example:
- Fox News is owned by Rupert Murdoch, who also owns a number of individual television stations, the Wall Street Journal, and the New York Post.
- Sinclair Broadcast Group owns 173 television stations and is in the process of expanding that to 233.
- McClatchy owns a a number of newspapers and has a service that provides national news.
- Reuters and the Associated Press also have services to provide national news to local media, particularly newspapers.
- Tronc owns multiple newspapers.
- Gannett produces USA Today and other papers.
- ABC is a television network that owns a number of individual television stations, and it is itself owned by Disney.
- Warner Media owns CNN. It owns other media outlets, but that's the main news organization.
As posted in a comment, Wikipedia has a list of media conglomerates. Not all of those are news.
The point being that the major organizations are owned separately. E.g. the New York Times and ABC have separate owners.
It's not entirely clear why the major news organizations often have such similar opinions. Part of it may relate to the locations of most of them. Major news organizations tend to be headquartered in cities and run by people in cities. Cities have a distinctly different politics than do suburban and rural areas.
There are only a few national news agencies like McClatchy DC, Reuters (international), and the Associated Press. As they will often be the first source that journalists see, their editorial opinions may color the original stories.
Another issue is that journalists are almost universally college graduates, and colleges have a distinct politics of their own.
Organizations like Fox News may exacerbate this, as they pull the small number of ideologically distinct people to themselves. This leaves fewer to work at other organizations.
While television anchors can be well paid, many of the jobs in the media pay much less. Low paid college graduates are more likely to be Democrats.
Due to how politics in the United States works, there are a large number of partisans who know some number of media employees. This can be an advantage when trying to insert a story into the narrative. And if the original source is partisan, it is unsurprising if most start from that partisan point of view.
