Because people partaking in the creation of this kind of videos, which is to say so called “video essays” do not posess the ability to syntethize their thoughts enough and need artificial padding to lenghten the video and thus give an allure of an thought-provoking essay.
Also “video game essays” are overrated and will over interpret a single mechanic over an hour.
Josh Strife Hayes manages to analyze several mechanics of a game, its context and 100% it in less than an hour.