And if it is an exceeding rare book, you probably don't want to be destroying it to scan it. I think it's possible to use a decent camera instead of a scanner, but it is still quite an involved process. Look at what Google did....

The books were placed in a custom-built mechanical cradle that adjusted the book spine in place while an array of lights and optical instruments scanned the two open pages. Each page would have two cameras directed at it capturing the image, while a range finder LIDAR overlaid a three-dimensional laser grid on the book's surface to capture the curvature of the paper. A human operator would turn the pages by hand, using a foot pedal to take the photographs. With no need to flatten the pages or align them perfectly, Google's system not only reached a remarkable efficiency and speed but also helped protect the fragile collections from being over-handled. Afterwards, the crude images went through three levels of processing: first, de-warping algorithms used the LIDAR data fix the pages' curvature. Then, optical character recognition (OCR) software transformed the raw images into text, and, lastly, another round of algorithms extracted page numbers, footnotes, illustrations and diagrams.

Would argue the opposite. If no one has shared it yet and it's not rare / valuable, saw it, use a double sided auto feed scanner, and share it.

Agree it's not too easy to do as a one off, but once you get the hang of it maybe more will come. I often have a hard time finding digital books so am in favor of more of this

It is a rare expensive book that I wish other can have access to. I don't want to break the spine of the book as I am still using it for my studies, can I not just scan each page of the book using my phone, then convert them into pdfs and merge? Is that a bad idea?