I think we all know this pace of rollout is a deliberate decision, and not a necessary approach. They could have spent the past two years working on all the individual parts of the organisation's branding.
But the font project started first. Then BBC Sport needed to rebrand before everything else was ready. Next came BBC Four and then BBC Two. News is next, and then possibly (hopefully) BBC One will get a rebrand using Reith.
For BBC News specifically, it is possible that there was a plan to launch the new graphics sooner, but things cropped up which delayed things, and so individual programmes were ready to change their logos, and they went ahead.
Let's hope they don't kill off those beautiful curve idents from BBC Two.
They're just amazing to look at
I don't know if you have noticed the BBC Two font with the curve idents is BBC Reith in the two forms standard and sans.
A random bunch of thoughts molded into person