I feel it's also a scaling issue: If you wanted to do all of the digital bookkeeping of today on paper, that would be perhaps impossible. I don't think personal note-taking is in any way a large contribution to paper use.
I do art on paper and even I don't go through 500 pages in a year. It's at work, things like 60 page reports that need to be printed for submission (and then get printed 2x or 3x again because you can replicate it).
The ease of printing documents is the culprit, you can just replicate large physical artifacts again and again. You can't do that with your personal notes that probably only exist as unique artifacts and maybe get scanned into a digital archive.
I do art on paper and even I don't go through 500 pages in a year. It's at work, things like 60 page reports that need to be printed for submission (and then get printed 2x or 3x again because you can replicate it).
The ease of printing documents is the culprit, you can just replicate large physical artifacts again and again. You can't do that with your personal notes that probably only exist as unique artifacts and maybe get scanned into a digital archive.