Screen size, target audience (1080p Zoom), cost, sensor size, and pixel size all come into play.
You can pump numbers for the sake of it on paper, but the reality is that it’s very hard to cram a good image sensor into a laptop screen in an economic way. There’s unfortunately just not enough real estate as thin as they are.
Meanwhile, phones are quite a bit thicker & cameras are a huge selling point. Plus, almost everyone has one. It makes sense that if you want higher quality video on your computer, you’d use the other device which has video higher up on the design priority list.
Darn, one piece of marketing BS getting in the way of other marketing BS. Yea, 1080p is plenty high res enough for your work meetings and family calls - but users don't really care about the thin aspect, we care about weight. Getting better key depth on laptops in exchange for a modicum of extra width is a deal I'd take any day of the week... and that'd allow far better cooling engineering and for a few more bulky components.
Beyond pure aesthetics thickness absolutely does matter when you are sticking your laptop into a backpack.
What surprised me was how long Apple was on 720p.
The other issue I didn’t bring up is the form factor. Phones and tablets simply have more room for a webcam than the MacBook Pro screen and I don’t actually know anybody shipping a laptop with a built-in 4K webcam. Mind you that Apple could ship a better camera with its studio display but opts not to.
But you’re not going to fit a really good lens on the laptop screen without an annoying bulge anyway, and for 99% of people it would be a waste to spend resources on it anyway.
Using the phone is a much better solution. People are likely to have a good camera there with an OK lens anyway.
It can be done without a bulge. But designers gonna design and make something ugly. Smartphone CMOS sensors are not bigger than the usual stuff in Laptop bezels.