Strange reason is right. Mmmm.

I don't think making your own carpet is a very good idea. It would never be as form-fitting as something made with the proper mold for the backing rubber/plastics.

There are a few sites which carry aftermarket replacement floor carpeting - either made from reverse-engineered molds or molds purchased used from the car companies.

You should be able to find a few of these using Google.com. Search for stuff like "car upholstery" "car carpeting" "custom car carpet" etc...

I was looking only for the actual carpet material while searching, so I didn't save any of those links, sorry.

Bruno