Not sure on the first. Apparently almost all alumninum is recycled, and reused, as its melting point is super low compared to most metals, so its not quite as wasteful as it seems at the first glance.
It’s probably not milled from a brick-shaped block, but a cast that approaches the intended shape.
iPhones are iPads have a milled CNC “unibody” as well… Being able to dictate where to have more thickness helps a ton on the luxury feel. Most of the chips are recycled anyway into new billets.
Unibody is a very appropriate technique for a small portable device that needs to be strong from force in many directions. It is overkill for a keyboard.
Overkill is the point. Same thing for iPads and iPhones. It gives a luxury feeling. That and Chinese manufacturing have made milling a very cost effective manufacturing method.
How would you make a low run product? Casting requires molds.
Other thick boxes like this are not made from a single block, for that specific reason. That's a manufacturing method most suitable for something relatively thin, like a phone/tablet/laptop chassis. This thing is a hulking monster compared to those.