In the 1980s, several Chinese medalists were stripped of their medals for using performance enhancing drugs. I believe China has learned their lesson for the most part, and they have enough good athletes that they don't really need to use roids.
Russia, however, has been slipping down the podium since 1992. They used to beat the US consistently, now they finished in 4th place in Rio. The state sponsored doping project was initiated to reclaim this lost glory, but unfortunately for them the IOC wasn't compliant and nearly had them banned. China has all the glory yet to attain, and so they do not dope.
I COULD BE WRONG THOUGH, don't take my word for it. Speculation.