Thinness has been frivolous aesthetics since Steve Jobs times. A thicker laptop will always mean better thermals, more silence, more battery, repairability, more ports.

In a laptop though that thinness and its compromises might actually provide some positives to the product: lower weight, easier to carry in hand or in a bag

On a desktop you view face on, who fucking cares how thin it is?

Its brand differentiation, and hoping that folks associate the ability to make thinner products as "better technology". Which they seem to, especially when paired with a high cost. I'd be surprised if one of their initial mockups didn't have a transparent bezel around the screen (or the screen itself!) to make it look like a minority-report style screen