Why do Radio 3 presenters adopt the tone stupid adults use when addressing children?

Anyone who has listened regularly to Radio 3 over the decades — not to mention the Third Programme, which Radio 3 replaced in 1967, and which provided an incomparable musical education for many of us — can’t have failed to notice the change in style and standard of presentation. Listening to any radio announcer from 50 years ago is bound to cause hilarity: carefully read scripts, un-emotional delivery; all told, quite like the Queen’s Christmas broadcast.