i am just going to say one thing. Sistar are digital monsters, does that fact have any reflection on their physical sales? no
so let's not act like public appeal is relevant to physical sales for kpop groups
lbr, quality has nothing to do with this. most fans don't buy albums because of quality but because they are fans and want to support their biases. they even preorder them before they know how the content sounds like. i am not saying everyone does that but come on, it is what most fans do. and this doesn't only apply for SJ or/and SNSD but for everyone no matter how much fans of less popular groups claim otherwise.