For metal-framed laptops, why do they use milled pieces of aluminium, and not stamped metal?

So they can ask a premium price?

Stamped metal twists and bends easier. Don’t want my laptop pieces spilling out when it twists.

Durability. Stamped isn’t as durable as milled.

And weight. Aluminum is light.

I’m just giving round numbers here. You can easily find the exact figures if you need them.
Aluminum is ⅓ the density of steel so for a given weight, Aluminum is 3x the thickness of steel. For bending moments the thickness is cubed, so Aluminum has the advantage of being 27x stiffer. BUT its modulus of elasticity is about ⅓ that of steel so the advantage is only 9x (or maybe 3x – i forget if it is a square term.)
It is difficult, if not impossible, to stamp Aluminum so it is usually milled.

Weight. And aluminum is more easily recycled.

I thought aluminum is soft, making it easier to stamp?

@raum It is brittle. You can stamp something like letters into it but bending 90 degrees will very likely break it. There are many different alloys and formulations so you probably can find one that could work.