I personally like a lot of Kpop for the strange music production that comes out of it with bands like Red Velvet, Mamamoo, Stellar, Lim Kim, Dalsooobin, Dal Shabet, etc., but that is really more of a side effect of Kpop's main product.
Albums are usually sold as boxes with a photo book inside and collectible cards, they are almost more like magazines. Some albums come in different editions with different idols featured - it's common for a fan to buy multiple copies of the same album in hopes of getting the edition or cards of their favourite idol (bias). The fans see album purchases and 'streaming' (playing their youtube singles on repeat) as ways to support their groups and increase their reputation.
Think of buying albums more like a kickstarter fundraising for fans to support their idols. The photo book or the chance to get a ticket for a fan meeting is arguably a bigger draw than that CD itself.
In fact, what I know, a lot of sales, especially oversee ones, those albums are not even physically sent back to the country where they originated at all. It is just a gesture to help their idols rank better on the music shows.