because Lucas conceived the film as a retelling of the serials of his youth and wanted to give kids a modern fairy tale mythology and has been quoted many times as saying so . George Lucas in an interview in the New York Times, published on the 12th of September 1976:
It's for young people. 'Graffiti' was for 16-year-olds; this is for 14-year-olds. Young people don't have a fantasy life anymore, not the way we did. All they've got is Kojak and Dirty Harry. There's all these kids running around wanting to be killer cops.
and the drawings appear to YOU to show that , again , conjecture on your part and not fact .
See also…In the cover story of the April 1977 issue of American Film, for example, Lucas is quoted as saying: “I decided I wanted to make a children’s movie, to go the Disney route”; because he had realised that “a whole generation was growing up without fairytales” (Zito, 1977: 9, 13).