It's not really a question of performance, it's more a question of viewership, China got insane viewership from what I heard, and they want to promote it since League Of Legends is insanely big out there.
Of course, they also need to follow the narrative of "we put more slots for the better region", so yeah, if the Chinese scene has good performance over the year, they'll add more slots over time, but it's all about developing the local scene, putting some light on it, rather than pure performance.

We could think this way about where the Masters are, we saw Istanbul, Tokyo, all to develop and show the scene from those countries, and bring some lights to the local scene.
Because having a big event where NA is sleeping, and EU is barely waking up to go to factory, doesn't make sense from a viewership perspective.