The Chinese are lying about their motivation.
That's clearly true. They are saying they want developers of Bitcoin Core to decide for the best of Bitcoin or some such doubletalk, but clearly they know that means blocks will remain small, which is what they want.
I think it is because they want to force transaction fees higher to maintain the block reward on the next block halving. Chinese are notoriously selfish and short-sighted (which is perhaps why they require a totalitarian govt to discipline them). For example, here in the Philippines they have the reputation of being misers and counting every penny and even firing a good employee if 1 penny is missing (or charging normal losses in a business to the employees, e.g. customer complains the food was incorrect and so the food has to be discard and redone).
I also agree with this too. Another way to say that is that the miners are on the side of wanting to support the "fee market".
Bottom line, the miners in China want small blocks, so that's what we are getting.