I can't speak for KORE, but most companies use metal because of appearance and it is hard to get complex bends out of Plastic. You really can't Mandrel bend Plastic, but you can make it out of a mould. Mould costs are usually much more expensive than mandrel bending metal piping.

SR is looking into getting Plastic CAI's made in various colors, but I'm not sure how that is going.

You can ceramic coat metal to reject heat on the outside and improve flow in the inside, however this usually adds about $50 per intake. If you were to have it done yourself, it would cost at least twice that.

Wrapping the intake with thermally resistant heat wrap is a good idea, and fairly cheap, but it looks like crap.

Since most people want a combination of speed and performance...the metal intake is the way of satisifying both desires. Plastic or Silocone intake may be superior in their thermal properties...but people also like metal due to it's inherent "quality" feel and look.

It is one part what the market wants, and one part what works...