Opposite to the title, CS was actually really huge in both countries during 1.5 and 1.6, and arguably the most popular FPS title in Korea. But Valve introducing Steam was detrimental. In Korea, how PC bangs should operate with Steam just killed the game there, and in China, Steam was equally unpopular. The result was the birth of several Korean CS- and CoD-lites, some of them becoming very popular in East Asia.
In Korea it was SA (the most shameless CS clone), in Japan and Taiwan that was AVA (actually great graphics for its time), and in China it was CF (also decently popular in BR). Valve's policy had the ripple effect of spawning numerous Korean counterparts of their most successful product which eventually harmed them badly in the East Asian market.
So the title actually is "why CSGO didn't do as well as CS 1.6 in East Asia".
Anyways, since these titles were much more popular than CS locally, no wonder China and Korea weren't really good in CS pro-scene. At least CS in China wasn't completely dead unlike in Korea. Despite that, if you look back, Korea did pretty great during the 1.6 days in international LAN with a Major win for one of its teams and a few runner-ups, and China had some decent results in CSGO LANs.
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