The big 3 isn't stealing all the attention like they did during the 2nd and 3rd gen.
SM: Red Velvet, while still extremely successful, are not the current trendy group. Meanwhile Aespa, who is, has not been very active.
YG: Their only group is Blackpink and like Aespa, is very rarely active. Baemon could, and likely will, change this.
JYP: Itzy has been able to keep success, but hasn't had the same massive general public appeal as their predecessors. Meanwhile Nmixx's concept is too bizarre. Things could change, but the weirdness of their songs prevented them from automatically reaching stardom.
But there's still a craving for girl groups in Korea. The lack of success from the established big 3 labels helped HYBE, who was already growing, continue to grow in a new market with NewJeans and Le sserafim. With IVE, I keep saying the stars perfectly aligned for their debut to launch them into stardom. Similar thing happened with (G)i-dle who have been able to just grow and grow with each release. Middle tier groups like Stayc and Fromis9 continue to grow as well. And even lower tier groups like H1-Key, CSR, TripleS, and Fifty Fifty have been able to establish themselves in Korea and internationally.
This would also explain why 3rd gen groups like Oh My Girl and Brave Girls were able to find success during the 4th gen.
Moral of the story is, if you have quality music, you can achieve success. Higher tier, middle tier, lower tier, previous gen, the thing all these girl groups have in common is getting noticed for the high quality of their music. Imo high quality music was not given much attention because people only cared about the top 5 groups in their respective gen (3rd gen fans were especially bad with this). Now more than ever, if you have a song people like, it will help the group achieve success. And that might explain be an explanation for why Kep1er has been underperforming. Even fans have been somewhat disappointed in the quality of their music, so they haven't been dominating as much as people were thinking. But it's not as much about brand anymore and more about quality. Which is a good thing.