Launch BBC News: Studio B

[Brekkie]

Simply put, because the audience assume that’s the end and switch over. 

Of course though that is absolute rubbish and the regional news usually outrated the national news anyway.   And now they stick a weather forecast before the end anyway and expect viewers to sit through that.

It doesn't need a long ending - just three or four pips is enough with a wide shot of the studio and an end to the need to have an awkward pause on the News Channel (and indeed on Breakfast at 8.59 when the NC opts out, often midway through an interview).