why are there not more downloadable audio books
I am sorry that you are finding it difficult to find the downloadable audiobooks. We have over 8000 titles in our downloadaable audio. Here is a link to all the titles by subject: https://omaha.overdrive.com/browse#format=audiobook If you are on our Overdrive website you can find it on the Subjects tab, then narrow to audiobooks.
It is more difficult to narrow to only audiobooks in the Libby App. If you look for a section titled Collections, you can choose between ebooks & audiobooks, and then by subject.
As with print books, ebooks tend to be more popular than their audio counterparts, which makes it harder to find the audio.
I hope that this helps you find what you are looking for a little more quickly.