Why are so many top Chinese players from the Northeast?

Hi guys! So I checked out where some of the top Chinese players from the past 25 years are from, and I saw a really significant number being from the three northeast provinces. Some big names that come to mind are Ma Long, Kong Linghui, Ma Lin, Wang Hao, Wang Chuqin, Guo Yue, Li Xiaoxia, Ding Ning, Feng Tianwei, Liu Shiwen, Chen Xingtong and Wang Yidi. Considering that the region holds less than 10% of Chinese population it's very interesting that almost half of their best players come from there. Also even the ones that aren't from the Northeast are almost exclusively from the northern parts, with very few exceptions. Does anyone know why is that so? Is it a cultural thing? Is it specifically about table tennis or sports in general? It would be really cool if anyone has any info!