Maybe she enjoys it? Kids especially ones leaning ASD tend to have these kind of obsessions. I don't think anyone can force a 6 year old to practice rubik's cube 2 hours a day.
I can assure you Chinese parents can very easily force 6yo to do anything 2 hours a day (she spends most likely more hours a day than they claim), what is she gonna do, what's her other alternative at this age?
Not to defend this, but to say I wouldn't blame China but instead the international culture of everybody that watches a video of children online or tv. Stop it, it is never for the enjoyment of the child, always the fucked up adults around them.
I always cringe when someone shows me a video of someone who has an amazing singing talent and it's some 7 year old...