Because of the first reason. It is a personal opinion about signing libraries, and my preference is to work with signed DLL's.
I can sign the assembly manually, but in the end, it will requires modifying the build process with an extra step (or doing it manually one time and adding it in my own source control system instead of the NuGet repo).
Just a note that this repository has moved to github now. See here for new repo.
All issues will be slowly migrated as well. If you still find this issue important, please provide your Github account so I can recreate this issue and link it to your Github account, otherwise I will simply close the issue.