My library co-op uses the same system, and while they do have books I want to read, they're often out of stock of the ebook. That irritates me enough to not borrow ebooks from them.
I have several ebooks for sale on Amazon. I tried to DONATE unlimited access to them to my local public library, and I cannot get them to return or even acknowledge my repeated emails about it.
Either way: given that many public libraries offer ebook rentals for free, Scribd should be marketing to them rather than directly to customers.