Prices are set six months before renewal and other circulation figures are known and 18 to 24 months before costs are in. As a result, price decisions may be influenced by economic events one or two years past. In short, if you wish to understand how a watch works, you really must look inside. Moreover, the commodity model is not appropriate for science journal subscriptions. If it were, journal rates would have fallen in response to reduced circulation.
Journals are, and always have been, published primarily for library usage.
The library subscription is, in essence, a site licence that allows for multiple access, and covers the rights libraries and their readers enjoy under fair use. The personal subscription rate was established much later in response to demand from individual researchers who wanted a copy for their own personal and private use. Most publishers then set a rate that recognised the difference between access by one individual personally, and the unlimited access afforded by the library subscription. What individual subscriptions can do, if the price is right, is increase the number of copies the publisher prints, thereby reducing the unit cost and helping to keep library subscription rates down. The question every publisher faces in setting prices is how to maintain a balance between institutional and individual rates.