As the league books a guy as being always around the knees / ground ball type of pitcher instead of batters thinking, "Fine, I will wait you out until you start bringing the ball up in the zone". Which they probably realize might not work because those pitchers WONT bring the ball up (why would they? Especially if they are established guys and the umps are giving them the low strike anyways, like Wang always gets). Maybe instead they think, " You wanna play it that way? All right I will just bring out the Branyan Golf Swing and see how you like giving up four bases at a time!". Which would result in the increased O-Swing% and ground balls. Also maybe batters book him and think, "You want a ground ball I'll give you a ground ball" instead of going away from what the pitcher is trying to do they go with it and get a screaming "ground Ball" up the middle that only bounces once and never gets more than 3 ft. off the ground. Which also brings up the selection bias of the scorers. They see Wang on the mound and think, "Here is a GB pitcher" and so they of course score anything close as a ground ball instead of a LD. Which probably makes GB % of established GB guys kind of useless.