I can think of three big ones (but overall about 6 are explained below), but essentially its for long term profit over streams and the money and industry rep they earn from it far outweights getting PAK's and any income generated from it, they likely save huge amounts of money at points so its no wonder newjeans can donate so much already.
1 - Its part of the artistic vision/marketing strategy. If they drop both at the same time people can listen without the MV. Alot of their music and concept plays into nostalgia, its easier to trigger that with visuals vs music alone, going for it too hard with the song risks the music sounding outdated. The gap is big enough that most of their audience would check out the MV and be influenced by the nostalgic look so even on future listens it gives the same feeling. Also for them, the artistic vision is becoming as important to their branding as the music is, there are few groups who managed to get that kind of branding right from the get go, best to emphasise it where they can and set themselves apart. By giving the visuals as high a billing as the music which draws in creative types and big IP who know their stuff will be given alot of focus and attention to details and prolongs the hype leading up to release and promo time without actually doing any extra work. The amount of discussion and fan theories surrounding MV's like cool with you were only possible because people watched it over and over and were forced to pay attention to the most minute detail, which we often don't do because the MV drops then we are running to check charting etc and all the creative details fall to the wayside. I mean PPG's? Murakami? big actors left and right? It only makes sense because the visuals are treated like an event within themselves and each MV is given its own time to shine away from streaming. This allows them to make multiple big deals with big names at the same time and assure them they'll each get lots of focus and when the digitals are release together, it makes the brands put effort into advertising their work with them and gives the album as a whole extra push without ador having to do anything.
2- YT relationship. YT is still trying to grow in Korea and worldwide, just looking at how much effort they put into advertising supershy should tell you alot. With the music being exclusively available to the majority through YT music, the only app you'd be able to listen through would be YT music. Which means more people may try the trial, download the app and potentially move from spotify or apple music. The market is tense between those big companies now so they are all trying everything to stand out. With their growing market cap in SK and the rise of kpop, it makes sense they are trying to secure a wider userbase by any means necessary, I don't doubt they likely paid newjeans to drop exclusive challenges on YT to compete with tik tok and YT may be paying them to do the delay drops even now or even promising them the algorithm will be nice to them. I remember a huge YT campaign around them for get up, I don't doubt YT was the one paying for it in exchange for them pushing YT music and shorts for supershy instead of apple music or tik tok, both of which would have made more sense at that time.
3- Ad deals. Many companies love to advertise and these days the most important thing is to know your target audience are tuning in, are likely to come back and to know a large volume of them are tuning in. The delay gives advertisers more security that the user base will come back, and since they will rewatch, it makes the product more likely to stick in your head. They are probs getting huge amounts of data that is hard to get in the industry which allows them to have better negotiation power with advertisers and potential sponsors. Remember the nike ditto ad? I imagine someone at nike was furious they didn't get involved sooner. Imagine the ad was dropped as the first teaser to that CB? It would have been insane promo for them, especially with how huge ditto ended up being. I bet thats one of the reasons why apple, coca cola and YT music went so hard for get up and it worked out well for them, 2 of 3 ended up winning advertising awards and YT's profile for shorts increase loads.
, even tho the camera 
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