This seems really strange to me since my local town has put out a news blitz about cardboard being nearly 100% recycleable. Not saying you're wrong, you clearly aren't. Just weird that more cardboard is being recycled but it's more expensive. I'd think the reverse would be true. More cardboard being recycled would mean that it would be cheaper.
Oh well. Nobody said the world made sense.
It is, but see, here's the thing people need to be aware of in the recycling biz.
When one make cardboard versus paper, the fibers are often coarser, and less refined.
When Paper is recycled it is made, I don't want to say worse, but the quality is in some ways diminished through the process:
Process
The process of waste paper recycling most often involves mixing used/old paper with water and chemicals to break it down. It is then chopped up and heated, which breaks it down further into strands of cellulose, a type of organic plant material; this resulting mixture is called pulp, or slurry. It is strained through screens, which remove any glue or plastic (especially from plastic-coated paper) that may still be in the mixture then cleaned, de-inked, bleached, and mixed with water. Then it can be made into new recycled paper.
So, the cardboard has been reduced, and can be made into new cardboard, but still that process is not cheap nor easy:
Recycling
Most types of "cardboard" are recyclable. Boards that are laminates, wax coated, or treated for wet-strength are often more difficult to recycle. Clean cardboard (i.e., cardboard that has not been subject to chemical coatings) "is usually worth recovering, although often the difference between the value it realizes and the cost of recovery is marginal". Cardboard can be recycled for industrial or domestic use. For example, cardboard may be composted or shredded for animal bedding.
So, when Cardboard is recycled it goes from Heavy Duty to less heavy duty, to ultimately either recycled note paper or tissue/toilet paper.
Take a look some time at the actual fibres of the various papers in your house.
Cardboard: Thick, Long Fibres
Writing Paper: Thin, short fibres
Tissue Paper/Toilet Paper: Thin, very fine, very short fibres.
Now remember what was said above; In Recycling the recovered paper product is chopped up and mixed with chemicals. So each step through the process is reducing what has come before.