"I'm thinking also to prevent idols from becoming hostile due to "being in an unsuccessful/inactive group" for the first 12 months or so from the start of the game. "
I think that may be a purposeful feature as of update 11: "Business proposals now affect graduations (idols like getting jobs and hate not getting jobs)"
I personally don't mind it, (I actually like it) and see it as no different as idols getting upset they aren't in singles when they (presumably) joined to sing and dance to songs. I think not releasing singles for six months is a weird case, I dont really see it as a shortcoming.