Why don't Bookshare books contain recorded human speech?

Bookshare has chosen to produce digital files that can be read with a range of text-to-speech (TTS) tools, rather than books that are human-narrated, to offer members the widest possible selection of materials as efficiently as possible. As a result, we can add thousands of books to our collection every month, including best-sellers that are often live in Bookshare on the same day they are available from commerical book sellers. Members can download books in multiple formats and customize their reading experience to make it work for them.

TTS voices are becoming more and more human-like, and the amount of content that can be read with TTS tools is growing exponentially every year. In addition, tools that support TTS reading have been shown to help students, especially those with learning disabilities, to improve their engagement, interest, motivation, and comprehension. For more on this topic, read "Reframing the Text-to-Speech vs Human Audio Debate: Both Make Reading Easier."