Market segmentation? High-end ones have to look "professional", I presume the thinking is you wouldn't give a serious boardroom presentation on a lime-colored laptop.
On the other hand, for students and schoolkids once you've solved "cheap", it's a plus to also tweak for "fun".
Speaking of market segmentation - this may vary by country but on https://www.apple.com/macbook-neo/ (US site accessed from EU VPN) if I scroll down a bit, what gender do you think the "blush" color is most associated with? Is it coincidence that the laptop is being held in a hand with painted nails? (And a wedding ring.)
I agree businesses would probably want dull laptops. But plenty of non corporate users would like color.
I’d still pick the MacBook Pro because it has an SD card slot which any photographer is going to want. I don’t need something that blends in at a board room.