1. cuz he is fed up with the elders treating him as a kid.
2. cuz he wants to grow both in his career and as a person
3. cuz he is sick of the big family and wants to lead a private life only with Suhana (looks a very remote possibility to me but u never no...in just one day governments can fall..Ishaan ko badalne mein toh ek sec kaafi hai)
Anyways lets see.