I bought a cat tree from the same company, and I have a similar issue with each product. While this is of better quality than anything you'll find in the big pet stores, it just doesn't appeal to my cats. The scratching posts they had were beyond well-used. I kept two, got rid of two, and chose this one because one cat would only scratch carpet, and the other only scratches sisal. Alas. No matter where I place this one, the cats continue to ignore it. 

The actual posts on the old scratchers are about 4 or 4.5" diameter; on this one, the sisal post is about 3.5" and the plain wood about 3" (though it's hard to gauge diameter). Maybe they prefer the wider scratching surface?

Or maybe they're just being cats. Sometimes there's just no predicting what the little furballs will find acceptable. 

Pros: well-made, stury
Cons: cats ignore it