I think if time on page and average session metrics suggested that's what people wanted, that's what we would see. It's like complaining about how the news reports on inane stuff.
Similar idea with news. The objectives of profit and conveying meaningful information aren't necessarily aligned.
Disregarding the subjectivity of 'meaningful,' the advice 'know your target audience' is good from both a product design and marketing presentation stand point.
Maybe it is possible to have a landing page that people leave much more quickly but that is more successful. Maybe it is possible to keep your audience informed without them watching for very long.