The idea that attention span is shortening, particularly among younger generations is a myth, and the claims are not backed by any evidence. The idea of an “average attention span” is a myth, as there is no such thing. Attention span is very much context-dependent.
Even within particular contexts, such as driving or listening to a lecture, there is zero evidence of a change among the public or between generations. By the way, there is also zero evidence that goldfish have a short attention span. The “eight-second attention span of a goldfish” is completely fabricated. Goldfish memory IS extensively studied, simply because the fish are easy to breed and keep, and in fact goldfish are known to be able to perform the same kind of learning as mammals and birds, and don’t have any specific learning or memory deficit.
It is true that shots and edits in film and media are getting shorter, but this has to do with changes the preferences of editors and tastes of consumers, and especially (in my opinion) much higher expectations among young people about the visual quality, animation, and compelling narrative in the media they consume. If the content is good, young people will binge-watch Game of Thrones or Stranger Things for days at a time.