I think its cheaper. Unfortunately its the reason most cat owners end up with scratching problems whether it be your walls or the sofa and unused scratching posts. Those kinds of materials are very nice for the cats claws. We never see the cat scratching on the carpeted floor however, because its just not a good surface for shedding the claw layers they need to shed (big purpose of scratching). Often we will see the cats scratch on door mats because they are usually a low grade material that provides more resistance to the claws.
If you go to cat shows they will usually have the *good* cat trees/posts made with great materials (bark, sisal, etc). We have one that is sisal wrapped and then have various corrugated cardboard in the house and no scratching problems on the furniture. The cat will learn that that is *his* place to scratch, and ultimately he knows you are frustrated, but he needs to scratch.
I hope the transition works for you but it could take a while to break the habit (just to warn you). I would spray something unappetizing in that area as you are retraining them to use the right spot. I find my cats dont' like the scent of lime, lemon or vinegar. This could deter them. THen use catnip on the new surfaces and do play sessions around the new objects since when cats get excited they like to scratch more (hence the ball track with carboard center i nice as they play with the ball they can scratch like crazy).
One of the most useful self-play toys in our household:http://www.petsmart.com/global/produ...N=2035764&Ne=2