I think you're severely underestimating the effort of digitizing it. Usually the way that's done is to break or saw off the spine and scan every page individually using a scanner, which is obviously a destructive process. Unless it's an exceedingly rare book it probably is not worth the effort.

Looking at pictures when trying to read is absurdly distracting, I wouldn't recommend just taking pictures. Instead, you can use a tool to convert a photo into a pdf document. It rips the text from the photo and types it for you. That enables you to just upload the text, which makes for a much smaller file size while having higher quality for the things that matter. But it's still very involved, you will definitely want to proofread the entire PDF to ensure it didn't make any errors.

Unlike that other guy, I think the less valuable a book is the more it needs to be digitized. An incredibly valuable book will be stored in a museum, and will likely be digitized if it needs to be and is capable of being. Whereas there are millions of books that don't get many copies and no one thinks to digitize them because they're not "important". That results in immeasurable amounts of lost media. Plus, if the book is cheap, then there shouldn't be any issue getting a second copy just to tear off the spine and scan it in, right?

Also worth noting, if the book is valuable and you do tear off the spine, there are a ton of places you can send the papers to and they'll make you a custom spine for the book and rebind it for you.

Anna's Archive (Currently located at [https://annas-archive.gd/]) would be my site of choice to share the book on! I can't comment on the scanning thing though, sorry about that.

When I would copy or scan books, I'd hold one page onto the scanner at a time, then crop and straighten each page in pdf before OCRing it.

I've scanned a book with my phone and uploaded to Z-Library before when it was a book I couldn't find online at all. Not a great quality pdf, but as someone who wanted to read the book for research and ended up having to buy a paper copy, I would've still preferred that pdf to nothing; it was still perfectly readable.

Like another commenter said, to get a good-quality pdf you'd have to take the spine off. Also note that it is really time-consuming and tedious to scan a book by hand (I assume there are machines that can automate it, but normal people don't have those). Big respect to people who do it regularly, but you may not want to be one of those people.