I think a big concern is that smaller groups aren't getting the airplay that they used too.
Combine that with the sales explosion not really trickling down and they're fighting for smaller and smaller pieces of the pie.
In order to break even and make a profit, purely on physical sales, an act needs to sell at minimum 70k, but on average they need to sell 100k albums.
Now take a look at the latest sales of everybody beneath the big 5 and the previous big 3 (Separating both collection of girl groups cause they'll always do numbers)
The next in line are
Itzy - 568,622
Nmixx - 759,888
StayC - 379,573
Now these are all excellent numbers, all three of these groups could survive pretty much forever off of numbers like this....
But then you have to consider. StayC, despite having the best digital performance in this group is firmly in 3rd place physical sales wise.
Going down a big more
Fromis9 - 190,594
Dreamcatcher - 126,507
Kep1er - 141,529
We're effectively out of the girl groups that chart realm and the drop off in sales is very very clear. These groups are making a profit, but they're making a profit almost entirely on physical sales and concert performances
Now look at everybody else
Billlie - 91,143
Kiss of Life - 59,092
H1-Key - 77,524
TripleS - 29,078
Purple Kiss - 17,058
Of these groups, only H1-key has managed to chart. And sales wise only H1-Key and Billlie manage to be outside the red zone