I would say it probably due to a lack of contentment within modern man. TV and media exploits this by advertisements that project this or that sense-object would bring everlasting bliss and joy to man, but it does not. And the search for contentment makes man go to extremes in terms of indulgence in sense-pleasures bringing out events which were previously thought to be unimaginable . The sickness has its origin in the lack of contentment within. The dumbness could be attributed to mental dullness brought about by an overload of sensory stimuli. The majority of the population, as Plato stated, are not intellectual. The majority is thus good target practice for propagandists taking advantage of their lack of intelligence. I have seen many horror films in 24 hour movie channels which have no brains whatsoever, and the only objective I can presume is to inject conditionings of fear and obedience in the unfortunate viewer.
TV. A great way to brainwash masses of people simultaneously. A subtle wash that is like candy in the gutter. Why eat it?