Jesus, do you have any sources (Chinese is fine) for this? This is horribly anti-consumer and I'm surprised there's not more of a push back if it's so common.
The resellers get paid a few dollars for the malware install. I think the most common is people reselling to ship out to other countries, and not sold in China itself.
The aliexpress shops get shut down, negative feedback, but they just open another. Note that aliexpress actually shuts these down in the first place and is "reputable" end of things. Never ever buy devices from gearbest, wish, etc. - ever .