The popularity of entertainment personalities has many variables, some of which cannot be easily explained. (People try anyway.) And their overseas status is often the function of factors that even the best analysts and pundits cannot fathom but, interestingly, may reflect certain cultural variances. For example, why do Chinese movie buffs swoon over Keira Knightley but not Reese Witherspoon? Both are movie-star gorgeous and both have acting chops to boot. You can cite the works they appear in because their public personas are invariably molded by the roles they take on. And the Pirates of the Caribbean franchise is certainly a widely watched platform for Knightley to strut her stuff.
But there is more than hit movies at work here. Shia LaBeouf and Mark Wahlberg are in the Transformers movies, which got astronomical returns at China's box office, yet their name recognition in China is probably less than that of Wentworth Miller, whose only memorable role is in Prison Break.
Like Ken Takakura, Miller was lucky that his TV series entered the Chinese realm at a special moment, in this case when video content began to be streamed or downloaded en masse and thus made available to a new generation growing up with the Internet. Had he appeared five years later, though, the impact would have been much diminished because Chinese netizens by then were swamped with a plethora of programming choices. Unlike Takakura, Miller turned out to be a one-trick pony who is largely forgotten in his own country.
In business parlance, both actors enjoyed first-mover advantage, coming into a market that had just been opened. Obviously, the meaning of "open" here is hard to define. Your movie could be screened in cinemas and fail to attract an audience of significant size, or it might not find any distributors but somehow stumble upon a huge following, often through a channel newly available and not yet noticed by mainstream distributors.