A question about Jedi training in Star Wars....

This question is directed to those who have detailed knowledge of the Star Wars franchise.According to offical canon,there are seven offical styles in lightsaber combat.Jedi master Oui-Gon-Jinn used an aggressive style called Ataru,while his one time apprentice Obi-Wan Kenobi employed a defensive style called Soresu.But to me,that didnt make sense.Since Jinn was Kenobis master,wouldn't it follow that he would teach him the style he used?Why would Obi-Wan use a different style?It would be like a marital artist whose sensei was a Karate master but he himself practiced Kung-Fu!