hard to say. at the beginning of the novel there are just a few song references playing a part in contributing to the evocation of the historical backdrop, later on they suddenly mushroom everywhere and, i can only speculate here, maybe his publisher's reader told him that they work well and that he should consider adding even more, and so he did, probably also doing his research on this subject matter, not to the disfavor of the story. the songs' function is widened later on in the story, inasmuch as they do not only evoke the backdrop of the 60s west coast but also shed more light on the characters, and even serve as slapstick stunts of knee-slapping quality. sometimes they are used ironically when the narrator, doc, during short phases of relative clear-headedness, is observing from a short distance his surrounding moronic culture and the oddball behaviour of his fellow dope contemporaries, these scenes are among the best in the novel