I think that news at 0700, 0800, 1300, 1700, 1800 is enough. On breakfast at times it sounds like a news programme interspersed with bits of music!
Sorry to be the contrary voice, but I think brief news bulletins on R3 are useful - at the very least they might alert you to something that you might want to hear about in more depth on Radio 4. And they also, sometimes? often?, feature more arts-related stories than R4 does.
The OP could have substituted "news" with "trailers". They are both the bane of modern broadcasting and Radio 3 should be a banality free zone, as it once was, of course. However, "they" would tell us that the bulletins were introduced in response to requests from listeners, and, of course, we know how responsive they are to us listeners.
As John W says, it's designed to stop people turning to R4, or other stations. Frankly, as they seem to have replaced one set of listeners with another, that might be true of the majority who do now listen to Breakfast.
But news? I mean can't you just go the BBC website or tune to R4 for 5 minutes and then switch back? You'd get your news fix and the rest of us could indulge ourselves in the pretence that the world has stopped for a few minutes.
if they did not broadcsat any news or trailers at all and put on the odd play ....?
We are free to do anything we like as long as it is UNIMPORTANT