Re: BBC documentaries
Part of the problem with programme material for the BBC is it has to fit the BBC time slot but may also be sold to other broadcasters who have shorter slots, especially advertising based channels. It is easier to make the programme for the shorter slot and pad it out than it is to cut to fit. Recaps fall after where ad breaks would appear and many may have been made for advertising channels in the first place.
I am sure the reason we have so many 'coming next' and other BBC self-promotions and pointless idents are to make imported programmes fit the artificial 'on the hour' programme start times we expect in the UK.