>The problem with these lab books is that they're often the personal property of the scientists and, as such, almost a sort of diary

Further complicating things, individual researchers don't actually own the books. Often, an institution or the lab owns the rights to the book. This can make individuals who are otherwise keen on "open science" hesitant to place copies of this information in a publicly accessible place.

See page 4 of this manual from the NIH (National Institutes of Health) about the ownership of notebooks.

https://www.training.nih.gov/assets/Lab_Notebook_508_%28new%...