Why did The Fountainhead become a best seller despite negative reviews?

Despite receiving generally negative reviews from critics, The Fountainhead achieved status as a best seller primarily through word of mouth among readers.1

The novel, which explores the struggle of an uncompromising architect against conformist mediocrity, resonated with audiences who were drawn to its themes of individualism and integrity. By championing the idea that an individual's own happiness is a principled moral purpose, the book found a dedicated following that propelled its commercial success despite the initial critical reception.12