There doesn't seem to be rhyme or reason to whether something is deemed to be 'notable'.
Worse, you put off people like the grandparent who actually attempt to contribute.
We all want accurate and reliable sources, but why not work with people, rather than just deleting? Or why not a 2 stage process. Have a staging area for pages that aren't good enough. Then promoted to wikipedia proper when good enough?
What happens in X years time, when that file format is 'notable'? You've lost the person most inclined to write the document, and lost historical context from a living document.
The BBC had a habit in its early days of reusing 'old' film. What could have been a treasure trove is now lost. I cant help feeling wikipedia is being similarly short sighted.
/rant (not aimed at you btw)
https://en.wikipedia.org/wiki/Wikipedia:Articles_for_creatio...
Drafts in AfC will not be deleted for being non-notable, but they will also not be indexed by search engines.
When a draft is ready to be published, a reviewer looks over it and ensures that it is properly cited, before moving it to the encyclopedia proper.
"Only experienced editors should ever create an article from scratch. Others should first create a draft page and build the article there."
And as you say they aren't indexed.
https://en.wikipedia.org/wiki/Help:Userspace_draft
Userspace drafts also won't be deleted for non-notability, and they can be published whenever the editor feels that they're ready.
Neither of the draft spaces on Wikipedia are indexed by search engines, because these staging areas generally aren't proofread by other editors.