It's probably because having a suntan is considered lower class in China - middle and upper class people tend to protect all of their skin from the sun at all times when outdoors, to remain as pale as possible and so appear wealthy. At least that is how my Chinese colleagues have previously explained it to me.

The same thing was true during certain historical periods in Europe and North America, but now things have changed again so that a suntan has become fashionable again in Western cultures, but this was not always the case.