Even if it made Transformers type money in China ($120 million) only a quarter of that would make it back to the studios.
Which is exactly why US movie studios are more concerned with the domestic box office totals.
Well yes and no. The domestic market is shrinking and prior revenue sources like DVD sales have dropped over a 3rd. Hollywood is making fewer movies but bigger "tent-pole" movies (giant budget films intended to support the bottom line like a tent pole).
There are also threats on the horizon like straight to streaming productions and a growing audience that doesn't go to the theater as much. It may not show right away but because costs of production have gotten higher (budgets) and revenue streams are being reduced the movie industry looks at foreign revenue as the lifeboat to save them. China by itself. The chinese box office has doubled in the past year or two and still has considerable room to grow. There's also the potential that home entertainment sales will grow in China as they decline in the US.
If a movie was big in China by the time a sequel is produced the revenue from that country could easily double and that doesn't count any renegotiation in box office split (that occured recently from 17% up to 25% and increased the number of big films which could be released).