User blog comment:Dtuck010/Theory why Nightwing, Miss Martian and Superboy didn't want to join the League/@comment-5061669-20120429004504

I believe the reason for the refusal to join the Justice League is because the three young heroes are not ready to move on. For Superboy it is likely an attempt to have an identity outside the shadow of Superman. For Nightwing it is probably the drive to be a leader and protect the Team. For Miss Martian it is probably a sense of belonging, since the Team is the only family she has outside Manhunter.