Except they do stream that’s the whole point lol.
It would be like a BG selling 700k in albums for one comeback, then another comeback selling 300k, then another comeback selling 500k, all within 2 years time. That's just not the same behavior. Fandoms are loyal - if they're not loyal, then they're not a fandom.
Digitally topping the charts with one song, then another song released 6 months later barely peaking in top 20 and dropping fast means casual listeners checked out the song but no longer bothered streaming if they didn't like it. BG fans don't listen to the songs first then decide they're not going to buy the album.