TCSO Question re: Books for Inmates

While flipping around online during lunch I wandered around some of the Thurston County pages, eventually finding a list of acceptable items that may be mailed to inmates. The list made sense, until the very final part:

  • Books and Magazines
  • No hard back books allowed.

  • A maximum of 3 each.

  • Must be mailed directly from a publisher or bookstore.

  • Become the property of the Thurston County Correctional Facility upon release of the individual.

I can understand everything except the final part. Why should the books become property of the facility when the individual's released? Is it to help pay for room and board?