The multi-author book Holocaust and Genocide Denial: A Contextual Perspective edited by Paul Behrens, Olaf Jensen and Nicholas Terry (2017) is a more recent publication on the development, incidence and encountering of Genocide Denial in general and Holocaust Denial specifically. The chapter Holocaust denial in the age of web 2.0 by Holocaust Controversies' Nick Terry is online available at google books. Its conclusion points out these seven reasons which "can be adduced for the decline of Holocaust denial":
1 Consistent social disapproval
2 Its political ineffectiveness
3 The ease of finding other ways of expressing anti-Semitism or delegitimising Israel
4 Loss of 'market share' to other conspiracy theories
5 Inability to cope with the volume of recent Holocaust research
6 Lack of novelty
7 The ageing of the 'movement'
(Behrens et al., Holocaust and Genocide Denial: A Contextual Perspective, p. 53)