I think it might be due to the age of the paper. The charcoal paper is nearly 20 years old. I only know that because it came from the very first paper sculpture I made back in school. The texture may have flattened a bit.
20 years old? I'm not impressed so much by the age as much as I am that you managed to keep it in a safe place all that time and still find it. I keep things safe forever but that doesn't necessarily mean I remember where I put it! Nevertheless, its effect is great.