Well, if USAID is their motivation, then its gonna come back online when Trump is gone, or when he changes his mind. And then its business as usual. Still, the BBC's main funding comes from the British government, so I doubt that USAID has much to do with this.It's more like since they're not getting USAID money anymore they have to stop talking bad about China. Otherwise if they say bad about China weather they get paid or not then why should Trump pay you? It's like what Joker says, if you're good at something never do it for free.
The BBC knows that their decade long anti-China campaign is running out of steam. Since positive China stories are trending very well these days, the BBC is more than likely, trying to appeal to the "China Good" crowd, hoping to influence them in the future.