By trying to make a product too similar to an Apple product a manufacturer would open the door wide open to valid criticism about being an Apple knockoff company. By doing something different, they have claim to their own identity. But since (almost) nobody can beat Apple at design, that difference manifests itself more in getting more performance per doller (=cheap construction) or lots of products with special features (e.g. gaming machines).

Also it takes time to develop mass production capacity for something with a very different manufacturing process.