Because it wants to scare you, not reassure you. If it had started, "We've been so successful in tracking down and treating the things that lead to heart disease, it may soon drop to second place leaving Cancer as the #1 cause of death." Then you would be all happy that you weren't going to die of a heart attack and realize that your risk of dying from cancer hadn't changed (actually its been going down as the cohort of major smokers leave the population). But who wants to feel good about this stuff really? :-)
There's plenty of cognitive dissonance now that the stuff that kills us anymore is the stuff we understand the least. Actuarial tables aren't something we can reason about intuitively.
I was shocked to learn that an nMRI (where the nuclear "n" is usually silent) doesn't involve radioactivity. Such careful PR to avoid confusion about electromagnetic radiation, and it didn't even work?
