Why are China so good at table tennis ?

it's a "sport" that doesn't require a lot of area or space like soccer, football, or baseball. considering how expensive and rare real estate is in China compared to building an arena or stadium, unfolding a ping pong table is a snap. 

Like Basketball in the USA or soccer in Brazil, table tennis is considered one of the main "national sports" in China, thus there is a massive pool of quality competition.

It was brought to China by the British much like how Baseball was brought to Japan by American, and like Baseball it just "clicked" with the national psyche.

Where Baseball appealed to Japan's love of order, structure and team play, table tennis seems to appeal the the Chinese love of intense, fast-paced competition (consider how the Chinese also excel at badminton and gambling).