One source of many.
Traditional books have something called the first-sale doctrine.
This means libraries can buy (print) books in bulk anywhere they want, and can lend them out for free.
Digital contents don't have this. You don't buy an ebook or a video game, you buy a license to use that material.
And usually the license comes with limitations (and can be removed from your "possession" at any time!)
For libraries this means that the rights or temporary, restrictive licenses. Libraries have to pay MORE for digital licenses because they're going to lend them out.
Is there any technical reason why I can't buy one (1) ebook and lend it out 5 times? No!
This scares the publishers.
So they implement artificial scarcity.
One Copy, One User
One copy, one user, just like a physical book. This was the original, reasonable, model libraries started to use. Alice returns an ebook, Bob can now check it out. Carol wants a copy too? Maybe the library buys an extra license.
But then greed came in. Now ebooks expire after they've been checked out too many times. 25 checkouts and then BAM, that license is no good anymore.
Or you can spend $$$$ on a perpetual license. Top seller with a short burst of interest? Buy a bunch of cheap licenses that expire in months.
Libraries are incompatible with modern capitalism.
Let's talk numbers: an ebook that I might buy for $15 costs the library $40, and while I "own" it forever, the library has to decide whether or not to renew the lease at the end of the period.
Audio books cost more: Obama's memoir costs $95 for a single perpetual license. The ebook cost $35, almost twice what the consumer version does.
This means it's more expensive for shared goods to exist. There are no public rights for digital works.
Our libraries are spending boatloads of taxpayer money on an ephemeral grift. Maybe that's a tad too strongly phrased, but this isn't sustainable.
Libraries aren't meant to turn a profit, and neither should they solely line the pockets of the only 4 big publishers we've allowed to exist. They're about public services.