It seems like ethos is the most important factor.

Ethos: The speaker's credibility and character
Pathos: The listener's emotions and empathy
Logos: Logical validity
They say this is what Aristotle said in rhetoric, and JYP has said something along similar lines...
I believe the reason Le Sserafim is maintaining its high momentum and staying at its peak (though the absolute peak hasn't even arrived yet) is because they have captured what is known as ethos.