CBBC is a ridiculous decision: it moves tv watching from being a shared, collective / family activity to pushing children onto individual screens.
It also means that, whilst it should all be suitable and appropriate for all children, conscientious parents are less able to keep an eye on the content. We've all seen concerns expressed when schools push or endorse certain controversial perspectives (some would say agendas) on various subjects, resulting in parents complaining and protesting. Much easier for kids to see something on their tablet or phone than on the big telly in the corner of the room they're sitting in with the rest of the family.
Both of those channels get very low viewers though - BBC4 gets on average 0.8% and CBBC gets 0.19% (CBeebies gets a lot more I believe).
I recall reading somewhere in the past that, when they're monitoring/calculating ratings of programmes, they don't actually include children in their figures. I presume the rules were originally set up before the days of widespread dedicated kids' TV, to ensure that figures weren't artificially boosted by, say, four kids doing their own thing in the living room whilst their mum is watching 'boring' Coronation Street, and thus counting it as five active viewers instead of just one; however, it turns the thinking completely on its head when it's TV for children.
I suppose most older kids might watch CBBC alone, and thus not be counted as viewers, whereas little ones watching CBeebies will have their parent(s) in the room looking after them, so then plenty of 'viewers' are recorded, albeit adults who aren't interested in watching the programme for themselves!
Radio 4 Extra is a great resource. It's meant to be a mixed bag, appealing to all kinds of people. On a typical day, there may be 23 hours of content that doesn't interest me at all, but one hour that I would actively choose as 'gold'. Of course, even if this is the case for everybody, each person's '23h boring/1h great' will be totally different.
I don't think it's designed for you to sit listening all day, but to check the listings in advance and listen again/catch up with a missed programme from Radio 4 in the week or to (re)discover a classic old gem or two.