Disney, for example, reported its highest quarterly profit ever on Tuesday, thanks to its massive blockbuster hit “Star War: The Force Awakens.” Chief executive Bob Iger said the company sold a staggering $3 billion in Star Wars merchandise in just three months, and saw growth at Disney’s theme parks and other units. And yet, the stock (DIS) sank by more than 6%, and it has lost 25% since November.

On Wednesday, Time Warner—which owns CNN, HBO and Turner Broadcasting—also reported generally better results than analysts were expecting, with profit up 8%. And yet, its stock also dropped after the news was released, and the share price (TWX) has given up more than 10% of its value this week alone. Between them, Time Warner and Disney have lost almost $40 billion in market value.

Viacom has also been hammered by investors, falling by a staggering 30% in just the past few days, in part because the company reported lower-than-expected results on Monday, with operating profit down 5.4%. In Viacom’s case, its descent has been accelerated by factors unique to the company, including concerns about a potential power struggle between CEO and chairman Philippe Dauman and Shari Redstone, daughter of Viacom’s controlling shareholder Sumner Redstone.

When you strip away the impact of uncertainty about control over Viacom’s assets, however, the company is suffering from the same factors that have pushed down both Disney and Time Warner—namely, fear that these media and entertainment giants are losing control over the future of broadcasting.

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Bernstein Research analyst Todd Juenger put this into words in a research report on Viacom, in which he said the company’s traditional hold on youth markets—through channels like Nickelodeon and MTV—is in danger. “We continue to hold the view that the old business of serving kids/teens with linear TV networks is doomed,” he wrote. “And the new business of serving kids/teens with on-demand, digitally delivered entertainment is unlikely to be won by Viacom.”

That’s a Viacom-specific comment, but the same general fear is floating over almost every traditional media company that relies on broadcast television assets, and has been for much of the past year. The phenomenon of “cord cutting”—or, even worse, younger audiences who never sign up for cable in the first place—is growing, and large parts of the traditional media and entertainment market are being snapped up by streaming services such as Netflix (NFLX), and alternative sources like YouTube.

This trend is affecting even the most hard-core parts of the traditional TV industry, the ones that seemed impervious to market fluctuations, such as ESPN. The sports network has been seen by many as the strongest channel in the TV universe, because live sports is such a massive draw for many people, and ESPN controls some of the most popular events in every sport.

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Despite this, however, even ESPN has seen a decline in subscribers over the past year—and that has had a very tangible impact on Disney’s bottom line, since about 45% of its profit comes from broadcasting assets like ESPN. And with every decline in those numbers, the billions that ESPN has paid for sporting rights over the next decade look more and more expensive.

Disney CEO Bob Iger explicitly rejected cord-cutting fears on the company’s conference call, saying the cord-cutting phenomenon has been overblown, and that the “cable bundle” will remain the dominant force in broadcasting for some time. He even hinted that Disney might someday offer ESPN as a streaming-style service similar to Netflix. But the company’s stock fell regardless.

Investors, it seems, are afraid that Iger and other media executives are being overly optimistic about a fundamental restructuring of their industry—and that the potential downside could be severe if they turn out to be wrong.