which lets you find if your library has a copy or to find a library that does. It's a trick. "There are no libraries with this title available that match your search criteria [my search criteria was 'all libraries']."
How about Sailors and Scholars: The centennial history of the U.S. Naval War College (https://archive.org/details/sailorsscholarsc00hatt)? It's not available from OverDrive. But then it's been donated to the IA and is freely available. But I'll bet the publishers want it deleted anyway.
Or Introduction to Information Retrieval? I would advise trying to borrow it as it's probably very out of date, but still kind of interesting. OverDrive lists it (https://www.overdrive.com/media/179471/introduction-to-infor...), but no libraries have it. Neither does the IA. Maybe I should scan and donate my copy.
Having system in place (90% of libraries do) doesn't mean all or even most of the books they have physical copies of are available in digital form. The question isn't whether libraries can lend digital books but if they are able to lend the same ones IA did. Just because 90% of people are capable of running doesn't mean that they can run as fast as Usain Bolt.
My memory tells me it was both. With libraries closed they were not able to provide adequate access to those with disabilities.