system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: Why can't cell phone manufacturers use carbon fibre to build phone body instead of plastic, ceramic, glass, etc. ?
gpt
They totally could. Why would they? Carbon fiber scratches fairly easily and can shatter. It's biggest advantage is being lightweight, which isn't super necessary for a tiny phone anyway.

Plastic's way cheaper and plenty durable. Glass is scratch resistant. Aluminum is strong.