It's my understanding that this is largely because of the carriers.

Phone and text spam filtering came to the iPhone in China long before it hit other countries. I only know a couple of people in China, and neither are in tech, but they say it's because spam was absolutely rampant so the government leaned on the carriers to fix it, and the iPhone spam filtering appeared a short time later.

There's no shortage of Chinese users on HN, so maybe one of them can explain further, or refute what I've been told.