it's a vicious cycle really...I don't think this will be different for the 4th gen or 5th gen even...life as an idol is super short ... it's kinda understandable as it is mostly teeangers and young adults who spend time and money on their idols...as they grow up they loose interest and move on
older groups simply are not as atractive to young ppl because the whole idol culture heavily focuses on selling love and pure image...it's barely possible with idols who are in their 30s
it's better to focus on acting and variety shows if you wannaave a longlasting career in k-entertainment business
At the same time, members in Idol group don't really have the time to spend much more time as idol either, at least when you are a member of a group. I mean, if you debut at age 20 and seven years later you are 27 with very little private life. If you want to date and have a family it's time to get going at age 27, sure you can wait some more years. But for girls getting close to 30 I would guess they would start to feel a bit "stressed" being a member of a Idol group making it difficult to date and have relationships.