What is the point in waiting? August is the last month of summer if they wait until September then they're going into fall and the whole vibe of their title track has to change...
if they have one.
It's all about the right timing. Summer is the comeback period. September is kinda dry. Perfect opportunity.
Also, don't forget that a producer left SM. Still some songs that were going to be released so that is a problem too
Also, we might see Wendy again soon (according to some talks) and ReveLuvs are nagging SM ever since Psycho for an OT5 release.
They can't just throw 2 groups back to debut a group.
Nothing's set. Waiting is better than releasing something when everyone is releasing things. Many girl groups who could have a similar concept are currently promoting or are about to debut/promote. Too many is not good.