Longevity sometimes matters in some places, but not in KPop.
I have argued a few times that it would have been much, much more beneficial for BTS to abandon K-O-R-E-A, set up a new base in another country, give a big middle finger to K-O-R-E-A-N incels who will whine until eternity and rake at least $5 billion or more. I have demonstrated that even if they operated for 20 more years since 2025 they will probably not see even half of that.
Not only BTS, but most idol groups have a 'shelf life'.
Fans of veteran groups may not like this idea but , I have to say, idol groups do get older. And, unlike Hong Kong where the Four Heavenly Kings still dominate when they are in their 60s, in Korea companies do debut newer acts, from which they can get more money since newer acts have to give more to the companies than older acts whose members to get to keep a lot of the earnings for themselves, and older acts are shelved and are asked to pend for itself like Super Junior, which is now run by Shindong with very little interference from SM itself.
Unlike Japan, where older acts do have followings which last for life, Korea doesn't have that kind of culture. There are revivals time to time but they are short lived. Already some members from less successful groups have turned into trot for their next stage of career.
The better known act will still retain some following. How much, who knows. But the fact that veteran groups will continue to retain a sizable following to sustain their post-peak careers does not fit KPop. There will be 'some' fans, but eventually the venues become smaller and smaller until it is not worth having events and that's when such acts finally breathe the last.
The practice of companies who begin to 'retire' acts in their 5th and 6th air to promote their newer acts is mistaken; that is when such acts do peak and can make the most amount. However, after that, newer fans stop coming in and maintaining established fans becomes superfluous.
(The singer who traveled to Japan with Lee Jongsuk is an exception, although her recent scandal might stop new fans from coming in. She is the one singer in the entire history of Korean Pop who managed that. Her example cannot be used for other acts who have multiple members and multiple interests.)