His last book was a group biography of three science-fiction authors (Robert Heinlein, L. Ron Hubbard, and Isaac Asimov) and the writer-editor John W. Campbell. These men, like Fuller, interpreted advances in specialized fields for the public, making forceful arguments about the future, which they said would be science-driven, tech-enabled, (mostly) better in every way. This worked, in part, because these guys had something: preternatural confidence, and personal charisma.
These sort of people, like L. Ron Hubbard, died off because of increased skepticism and increased transparency. After ww2 you had this huge credulous population, and with considerable purchasing power due the post-war property and economic boom. The internet, and scandals such as Watergate and perceived hypocrisy of religious and political leaders and institutions, made people more skeptical overall, and also made it easier for people to verify claims.