Answer:
Because each of those mediums has a different logic.
Step-by-step explanation:
For journalists in television, time is a great constraint, and therefore, they are interested in news reporting that is succint, and even entertaining.
In newspapers, what is limited is not time, but word space. Journalists are worried about presenting a newstory with the right words, but without an excessive amount of them.
Finally, in radio, journalists are worried about presenting a newscast with clear words, and in a way that the listener can understand, because radio lacks the visual clues that are present in newspapers and television.