With old media (specifically television and newsprint) "information bandwidth" was restricted to a limited number of channels and pages. This meant there had to be a calculation where the editors had to maximize the audience by making the content short enough to not lose the easily distracted, but long enough to be engaging.

High-speed internet has blown open the information bandwidth cap so that now content can be created for every attention niche. This is just anecdotal, but it seems to me part of the decline of traditional journalism has to do with article length. People either want short, snappy headlines that tell them the essential information, or long, elaborately-written pieces thousands of words long. The only reason mid-length articles existed before was a compromise between the two groups.