How do you ever get that idea? people only watch MV one time if they dislike the song and are very likely to listen again EVEN IF THEY HAVEN'T LIKED as long YouTube keep recommending it and the user don't bother blocked the video
How do you think MVs like Shape of You got 5 billion views? Do you think every YT user watched it twice or even thrice?
The reason why views of kpop groups drop like rocks is because fans streaming nonstop in the first days but nobody can keep streaming songs for their whole life, people have social lifes and other things to do, once the initial hype is gone fans move away from their zombie streaming habits
You seems to be really convinced over 80 million people watched Blackpink or BTS MVs in the first day? The most likely number is 10 million people watched them, majority of this 10 million are casuals watching 1/2 times which could make 15-20 million views in first day.
The bulk of the views however comes from fans streaming 10, 20, 50 times a day. I'm not staying fans are using bots or doing anything illegal, they can do it as long it's not cheating nor harming anybody, but that's how kpop MVs works
shape of you is not your average western hit song. it was a super viral global hit song. it got heavy rotation on radio all around the world. it was loved by many people and a song like that i would imagine did get a lot of repeat views from a lot people. but most western hits don't really get that much views like for example rain on me and say so havent even reached 300M views yet.
im not denying that fandom streaming plays a role im just saying general public/casual fan interest plays a big role too. its like the same thing that happens on korean charts. seventeen/exo have big korean fandoms, more than most girl groups but they can't chart good because the general public isn't interested. same reason why they don't get a lot of views. its not that the fandoms don't care its just they can't