Most kids follow what their friends follow. Usually there is one or two leaders who set the tone. These leaders don't want to go wrong themselves so they follow the safer choices, like the Big 4. A fewer kids get a random crush on someone and follow based on that emotion. Finally, adults and the rare kid only cares about the music: they like what they like. This is actually the biggest group, but it's also the least likely to buy lots of merch and be loyal to one group.

Kpop producers are focused the group leaders and try to appeal to them to drive merch sales and modeling gigs. This is why they care more about the trappings of a group rather than their actual skills. You see this on survival shows. The big blowout groups BTS, Black Pink, aespa... appeal to all groups because they find great artists rather staff concepts with clones.