It would be hard to name just one single reason traditional media are in trouble. In fact, there are several forces at work. Users are shifting attention to newer formats: getting news online rather than from newspapers, for example.
Then there is the shift of revenue: with classifieds now cannibalized by online sources, newspaper economics no longer are viable, as display ads and subscriptions always fall short of what is needed to product the product if classified revenue is pressured.
There are more subtle forces at work as well. "Push" marketing, which tends to drive display advertising, is not working as well as it used to. Other formats offer hope of better results, and most of those are Internet mediated.
Information richness now is the order of the day, so there simply are other ways to learn things, again typically mediated by Internet and mobile mechanisms. That means less "need" for traditional media.
Also, many if not most companies have discovered that the traditional media role has blurred. Companies can themselves become content creators, aggregating their own audiences. To a large extent, it now is true that "anybody can become a content creator."
That means less money will be spent on traditional advertising, and more on creation of content, which is the foundation for "pull" marketing. Instead of pushing messages at people who may be unwilling to receive them, companies are inviting users to participate by creating interesting content in various ways.
All of those forces now are at work.