If true, it was quite a long time ago -- advertising has been the dominant source of revenue, and media has served that revenue source for a long time. Even in the days when print newspapers were strong, their "paid circulation" wasn't important because it brought in a lot of revenue, it was important because advertisers viewed it as the best indicator of engaged audience.
For-profit businesses serve their owners and generally act to maximize profits; there are exceptions, but expecting something different to be the norm without any structurally-imposed constraints mandating is naïve.
If you want a media whose mission is educating the public, You aren't going to get it from privately-owned, for-profit, media corporations because "educating the public" isn't something they can monetize as well as providing a combination of both a source of distress and the appearance of a salve for that distress for a targeted demographic to get them dependent, and then selling advertising access targeted to that demographic.