How do you publish a research paper? Unlike book publishing where authors, as a general rule, get advances, you first have to write it. You then submit it to a journal, and after a long process of refereeing and possible rejection it may eventually go to press, with the quality of the journal lending gravitas to promotion and salary decisions.
In this important system, all the work, from submission, refereeing, editing, and final acceptance, is done by academics at universities. Many of the journals appear under the imprimatur of academic publishing houses, and as academics now typeset their own papers using modern technical software the publisher's costs have come down in recent years. Yet strangely the price of some journals from commercial publishers has risen, and this at a time when papers appear on the internet well before printed versions arrive in libraries.
As far as costs go, mathematics is an extreme case because of its very complicated notation: matrices, arrows, sub-superscripts, and strange symbols. But with the advent of automatic typesetting, mathematicians have become incensed by the pricing policies of some commercial publishers.
The frustration has built over a long time. In 2006 the entire editorial board of an important mathematics journal called Topology resigned. They were seriously annoyed at the pricing of a journal, published by the Dutch academic publisher Elsevier, for which they were working without pay. Just to give an idea of prices, in 2007 the Annals of Mathematics, published by Princeton University Press, cost $0.13 per page. By contrast, ten Elsevier mathematics journals cost $1.30 per page or more.