So it is not like the regulations are saying "you must shift the coordinates by this amount", which would be stupid. It's just that foreign map publishers have not obtained the license to use the correct datum for Mainland China, so they make do with another one.
Wikipedia: "GCJ-02 (colloquially Mars Coordinates, officially Chinese: 地形图非线性保密处理算法; lit. 'Topographic map non-linear confidentiality algorithm') is a geodetic datum formulated by the Chinese State Bureau of Surveying and Mapping and based on WGS-84. It uses an obfuscation algorithm which adds apparently random offsets to both the latitude and longitude, with the alleged goal of improving national security."
What I don't completely understand, for two reasons, is why foreign map publishers would allow this pseudorandom offset to exist on their mapping apps:
1. The obfuscation algorithm has basically been cracked.
2. I don't think the Chinese gov can do much about foreign companies, except maybe by proxy, by pressuring the national trade liaisons or some such.
Google famously left China, but still has offices there. It's impossible to ignore China if you want to develop the OS that runs on so many phones manufactured there (though I believe Google's own phones are built elsewhere). Apple obviously is completely reliant on China almost to a crazy degree. Microsoft caved to China on censorship to keep Bing from being blocked, they never left the way Google did. Facebook doesn't cooperate with China at all in their software products which are all banned, but they're increasingly getting into hardware and can't manufacture their hardware products without China.