Obviously because it alludes at the "books of secret knowledge" of yore, hard to find books, compiled by masters of some domain and filled with useful knowledge.

It's like calling your Chinese restaurant "Golden Palace". It's not golden and its not a palace. It's just meant to convey "typical chinese", "luxury", etc.

I chalk it up to wanting an attractive title. The information is not actually secret in that the reader or writer is bound to keep the information secret. Rather, the knowledge was previously difficult (to some degree) to come by, and is now co-located, thus lifting the shroud of secrecy (by obscurity).

It's the same as code names that describe exactly what a project is about leaving no doubt about its purpose.

It creates enough mystery for someone to open the github page so they can read "intended for everyone"?

Because for me it was secret knowledge? And I wanted to share this knowledge with others?