A fraction has been digitized, and most of it still quite poorly scanned.
Try reading some, try actually using any of the schematics and other technucal drawings, a lot looks ok at a glance, then turns out to be merely better tgan nothing when you actually try to use it the same way you would have used the original.
Every few years the definition of practical scanner quality and file size increases by 2x or more. A fax quality scan is infinitely better than nothing, so it's great that such scans were made as soon as that became possible, but a few years later scanners became 10x better and it became practical to work with 10x larger file sizes. So all of those documents really need to be scanned again. And the same process needs to hapoen yey again at least one more time. Even very good scans from only a few years ago are still only good compared to old scans. They are still practically garbage compared to the original print.
And much of what is currently digitized is precarious, one lawsuit or lapse in funding or ceo decision away from the service being shut down.
I've already lost tons of stuff I actually paid for to services that no longer exist, let alone free services.
Right now a lot of eggs are in archive.org and they are a charity that paints a huge "kill me" target on their own back every day. It makes no sense to operate on the assumption they will never become the library of alexandria.
Digitizing existing printed material is not remotely a done job. Not even barely scratched the surface if you step back and look at how we are still in the first few seconds of eternity.