No one suspected this was incrementally assisting in the commodification of knowledge, at a cost to be born by the next generation of scholars. The idea of the fee originally was to pay for microfilming or the production of paper printouts and binding, as well as maintaining indexes, now sold as tools to university libraries. With microfilm OCR and pdf conversion that knowledge can now be stored as digital media and easily reproduced once the cost of digitization is dealt with. In the 1950s this was all setup to facilitate the easy scholarly access to knowledge. It was simply difficult to get other people's work without travel.
Most dissertations have only limited requests for copying.
However neither UMI nor NLC publish statements regarding quantities reproduced per item. The numbers may be high for core work in the sciences, a dissertation on genomes, or fibreoptics, AIDS research, or other cutting edge commercially valuable work. As an author of work in the system I have never received and information on royalty agreements or statements of accounting regarding publication from any university, national library, UMI or other third parties. I also find it interesting that even if there were such an agreement, the preceding generations of deceased scholars would not benefit. The profits from those dissertations will accrue only to the publisher, not to, for example, a trust account for scholarships at the institution from which the dissertation was granted.