This to me is not a very satisfying explanation.
Certainly, there are others artists who have good music (which itself is very subjective), are good performers, and are likable, right?
they have a star quality (imo) all of them have different personalities and complement each other. I guess you can say they have a good dynamic together.
They are also very relatable and as much as people complain they don't do much fanservice or communicate with us all the time and that's exactly make them look more genuine they only update us when they really want it's not forced.
Another thing is their sense of fashion a lot of young women look up to them and aspire to be like them (including younger female idols)