If you ask "why did it influence more people than Gellner's book on natl'sm, or Hobsbawm's, or Hirschi's, or Fukuyama's", idk: those books are better. But Anderson def. articulates the best and clearest case for one noteworthy hyp. about natl'sm.
btw, I don't remember Anderson attributing Pacific Rim nationalism to the colonialists themselves. IIRC the motif in the last ch was transition from priestly language to vernacular language, which was mediated in many cases by imperialists forcing mod'zn of ed. and central unis