https://pmcvariety.files.wordpress.com/2015/12/star-wars-chi...
[Citation needed]
[Substantiation needed to show that marketing materials for films can be changed that quickly]
It's a poster. You take it to a printing press and ask for a few thousand new ones, it's NBD. If they didn't already have several alternate designs from before they selected this one, it's like an hour of mucking around in adobe CS to make Finn smaller and droids bigger, less if you have the original images on hand.
The Force Awakens:
US Box: $937M
Foreign Box: $1.132M
Chinese Box: $124M
The Black Panther:
US Box: $700M
Foreign Box: $647M
Chinese Box: $105M
The Black Panther outperformed in China compared to The Force Awakens as a % of it's domestic box office and as a % of it's total foreign box office.
I'd imagine they might have just seen Princess Leia/Han Solo as more recognizable on the posters for an audience that might not be into Star Wars as much as other audiences seem to be.