The corporatization of the news media literally started with Richard Nixon and Roger Ailes who eventually found Rupert Murdoch to fund their vision with Fox News.

You know why they wanted to start their own media organization? Because they didn't like public broadcasting, the organization for public broadcasting, the organization created by Lyndon B Johnson and Congress to fund public media (which helps fund NPR and PBS). They thought that public broadcasting would favor Democrats too much (you know that whole the truth has a liberal bias thing). So they decided to create a media organization in which they could control the narrative instead of letting independent journalists do their job.

It took until 1996 for them to get everything together with Rupert Murdoch and the rest is history. The corporatization of other media outlets was in direct response to how Fox News ran their business because they cared more about ratings and making money than actual journalism, which caused the other news media organizations to follow suit.

So you could very much make the argument that Fox News was the root of the issue, depending on how you look at it. You can either say Fox News ruined the atmosphere around journalism and they started the backslide on the slippery slope, or you can argue that it was an inevitable outcome of deregulation. It becomes a philosophical argument at that point.

Do you know why Roger Ailes and Rupert Murdoch launched Fox News in 1996? Because on January 3, 1996 the Telecommunications act of 1996 was enacted. This completely deregulated the American media market and led to market concentration and is the reason corporations like Sinclair now reach 39% of the American market. (The max reach they are legally allowed to have). Murdoch announced Fox News less than a month later on January 31st, 1996 before Clinton had even signed the bill into law.

So even if you think the outcome was inevitable, Fox News certainly jumped on it faster than anyone else and were the ones to start the enshittification of news media.