It seems to be necessary on news programs to have someone at the scene
of the news for no apparent reason.

T'other night it was "Now over to Fred Bloggs at Hove Crown Court". As
it was 6:45 the court was closed so there was no point in Fred being there.

However, why is there such a long delay between the studio presenter
saying "Whats happening" and Fred replying?

With modern communication I can't see why there should be any delay at all.