100-word version:
In high school I played squash and tennis because they were fun and they also served as a diversion from the overly emphasized college admissions process in Korea...

 

120-word version:
In high school I played squash and tennis not only because they were fun but also because they provided me with the means to escape from the overly emphasized college admissions process in Korea...

 

172-word version:
In high school I played club squash and tennis not only because they were fun but also because they provided me with the means to escape from the excessively overemphasized college admissions process in Korea...