Manchester United did not sign Park Ji-Sung for purely footballing reasons. Shinji Kagawa was also not at Old Trafford solely because of what he could deliver between the white lines. The same could be said for Park Chu-Young at Arsenal.
While all these players offered varying degrees of utility to their respective teams and eras, their signings were not exclusively based on their ability. The modern football world is as much a business one as it is a sporting one, and these acquisitions had as much to do about business as they did football.
Man. Utd are subsequently the most popular team in East Asia, Korea and Japan specifically.