For mamamoo, their success was mostly based on their talent, their charisma and their music. their bad songs flopped. For Gfriend they had a huge buzz when they debuted and have been releasing public friendly songs all along. But when their song were not public friendly anymore they flopped because again they don't have a hit girl that gathers GP's attention to the group in general, even with a mega bomb hit song like MAGO.
Apink is a great example of how a hit girl can gather hype around a group even years after their debut along public friendly songs indeed but still. Without Naeun, I think Apink would have flopped long ago too.
Also for itzy, i'm not saying Yuna is not pretty, she is. But she is nowhere near Tzuyu or Suzy level, that's what I said. Not only in term of visuals but also in term of relevance. but of course she gets recognition as one of the visuals of the 4th gen and a member of a trendy JYP gg.
And of course Ryujin is really pretty again, but her aura isn't really hit girl kind of aura smh, like "i'm hot look at me!", she has very boyish charms. She's still amazing tho.
Regardless, i think If Yeji was better promoted and more hyped since the start instead of Yuna, she could have gotten really big specially if they also got a mega it song like Cheer up. I don't doubt she gould have become a hit girl.
So what i'm saying is that yeah their pretty, but overall as a group the harmony is lacking and there are more flamboyant visuals.
so in conclusion what i think is that they don't have a hit girl and a hit song. so their hyped died down.
anyway, i don't want to hurt anyone, it's just my analysis and it could be wrong of course 
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