Publishers of academic journals have a great thing going. They generally don't pay for the articles they publish, or for the primary editing and peer reviewing essential to preparing them for publication (they do fork over some money for copy editing). Most of this gratis labor is performed by employees of academic institutions. Those institutions, along with government agencies and foundations, also fund all the research that these journal articles are based upon.
Yet the journal publishers are able to get authors to sign over copyright to this content, and sell it in the form of subscriptions to university libraries. Most journals are now delivered in electronic form, which you think would cut the cost, but no, the price has been going up and up: