Comment by avidphantasm

Plastic is made from oil, and has limited recyclability (the polymers degrade so at best you only down cycle). Aluminum is one of the most abundant materials in the earth’s crust, and once refined is basically infinitely recyclable (or so the story goes). Aluminum is also reasonable light and strong, with good thermal properties (if your laptop chassis gets too hot, it has other design issues at this point IMO).