Matt explains why:
Essentially the Google Disavow tool is nothing more than a glorified crowd sourcing project.
Why try to identify low quality links via algorithmic signals when you can get an army of millions of webmasters around the world to do it for you?
And what better way to motivate that army than by telling them if they do all this work it will helpthem?
It's nothing more than a bulk snitching tool dressed up as a solution to a problem it doesn't actually solve.