The thing about high K pitchers is that if a pitcher is striking out a lot of batters, then obviously the batters are not putting the ball in play. As you mentioned before, if a batter puts the ball in play, many things can happen. A pitcher also then has to rely on his defense, which may or may not make the play. There are many possible things that can happen that do not result in an out.
It's all about the "out" here CP. An out is an out, so it doesn't matter much whether than out comes via the K, a ground out, or a pop up.