The 20-year-old says he wants to play regularly at the BayArena after sealing a €10 million move from Hamburg earlier this week
The 20-year-old was linked with a variety of clubs after enjoying a spectacular season at the Imtech Arena and says he rejected the advances of the Champions League runners-up to play regular football.
"I wanted to stay in the Bundesliga and Leverkusen and Dortmund wanted me," he told reporters.
"Both teams play in the Champions League but I thought Dortmund would use rotation more than Leverkusen. That's why I chose Leverkusen over Dortmund. It's really important to play regularly in my age.
"Any player would want to play in the big games in the Champions League. I know there will still be plenty of competition at Leverkusen and I will prepare for the season well and try to put in good performances when it begins."
Son also said he was flattered to be compared to fellow South Korean Cha Bum-Kun, who also spent the final six years of his career at B04 during the 1980s.
"It's already an honour for me to be mentioned with a legend like Cha. I feel the pressure but I'll do my best to satisfy the fans expectations of me."