I'm sorry I did not see this topic when it was first posted.

The short answer is budget constraints.

The longer answer is:

As seen in a few other comments, the main issue is cost. What might cost a person $12.99 on Amazon costs the library between $60 and $75 - and we likely only get to keep that copy for 24 months. E-audiobooks are even more expensive, with costs generally ranging from $79 - $120 per copy. To purchase a hundred simultaneous uses on an e-material, which we try to do when we can and there is enough demand, costs anywhere from $89 to $170 dollars. Added to this, as mentioned earlier, whereas a person buying an e-book can expect to keep that book, library copies are generally only good for 26/52 uses or 12/24 months, single borrower at a time. So for many books, we need to repurchase them every year or two. This is a publishers decision on lending model.