The decline of terms regarding anarchism is due to Margaret Anderson's determination to no longer "preach" the tenets of anarchy. She confesses that she was naive to think anarchism could actually happen and iniate social changes. This confession sounds defeated, but I don't think she loses her interest in anarchism.
Anderson's sense of anarchism superficially change to something more similar to individualism. For her, anarchy was always about individual enlightenment and improvement. She never lost sight of the need for this and often explains this same concept whenever she talks about being bored with conventionalities. Her early attachment to anarchy was due to anarchy's close relationship to individuality and non-conformity. She later develops her own understanding of individuality that continues the same concept that first drew her to anarchism. Emma Goldman, a famous anarchist, first attracted Anderson to anarchism and their relationship eventually fell apart as Anderson became more focused on "Art," and more specifically form.
This article, which actually predates the first link, claims that anarchism and art are connected by the same motivating principles. Although she later admits that anarchism cannot instigate change, it seems that she has just transfered her energies from propagandizing anarchism to focusing on the aesthetic form that anarchy should take: irony. This explains the n-gram of The Little Review that visualizes the decline of anarchy-terms and the rise, or at least spikes, in the usage of irony.
The Words Trend graph provides an easy way to locate the uses of irony that occur in these two spikes. I would have to read these volumes to find their specific usage and context, but that's much easier than reading through the entire run start to finish. I had read most of The Little Review on the MJP for another class and chose these terms to see how accurately they matched my own thesis. I marked TLR 4.4 as the last issue to really approach anarchy directly and Voyant tools seems to agree.
I will need to read these volumes that mention irony more than the others to get a better sense of how TLR envisioned the political registers of this aesthetic.