The development of minigames in China can be traced back to 2003, when platforms like 4399, 7k7k, and Xuan Xuan started out. 4399 became well-known thanks to hao123's promotion; it was almost impossible for it not to become famous. 7k7k only started running a lot of advertisements last year, flooding Baidu with ads and spending what must have been a fortune. As for Xuan Xuan Flash now, while its traffic is decent, the site's overall structure isn't entirely focused on Flash minigames, so its traffic likely can't compare with 7k7k or 4399.
In fact, there are many people who play minigames, most of them being children. Nowadays, kids play everything—games are everywhere. Creating a minigame website is simple: write some scraping rules, make the templates look nice, and you're done. However, building a well-known minigame site is difficult. Why? Because making a minigame site is too easy, they're everywhere.