[DTV]

World News America is individual programme paid for by a number of parties. Therefore if BBC (UK) does not pay towards it, it cannot be broadcast.

I'm not sure this rule really applies anymore, my understanding is that the new channel works on a basically one pot basis. 

I suspect the reason is more prosaic - I doubt it's really been thought about and, if it has, they will have chosen to keep UK content over it, as Radio_man suggests. There certainly could be room for it on the channel and it did always rate well during the few weeks of the year it appeared. But I guess that all speaks to the fairly muddled approach that has been taken to the channel. That said, though, I have been disappointed by WNA the last few times I've caught it - it seems to have adopted the same pacing issues that the rest of the channel suffers from.