There are about 129,864,880 books in the entire world. The median length for all books is about 68000 words. It would roughly translate into 250 manuscript pages in average.
If you must know, it would take 247 years for one scanner to do its magic and digitalize all the books ever written.
Ps: Pretty sure I screwed something along the way, would appreciate if you don't roast me for my math :v
ps. amount of information in the world doubles roughly every few years, I wonder how that reflects on the number of books.
For some people, freedom to try to express themselves and/or freedom to hear others try to express themselves is far more valuable than whether or not the writing is grammatically correct and typo-free.
The 300k figure has been very consistent since the 1950s, and is even down somewhat from the 1970s / 1980s IIRC (US LoC annual report data).
So the total is only up by at most about 10-15m books, and if you're looking at traditional publishing, about 3m.
The quality of books published is another question.