They *are* terribly common in tech industry C-Suites.
And when I say that I don't just mean people with narcissistic and selfish personalities; there are a lot of those everywhere. I mean people with the actual mental disorder. And it isn't common in the general population at all; less than 1 in 200 people fit the DSM-5 diagnosis. (Malignant narcissists are often diagnosed as psychopaths.)
They are also over-represented in the medical field and the military. No surprises there!