with the Chinese, blame the Beijing OG.
As the host country has a team qualified in every discipline they started to conscientiously learn any sport they werent so proficient in. i suspect the results in some sports just show up 4 years later.
As about the focus on the gold medals, i can speculate that's a communist habit. It was the same in Romania before 1989. Even I can say about myself that it took me a lot of time to start to appreciate the other medals too