it was about the appearance of the character, not about the personality, anon. norman bates was intended to be a somewhat attractive young man in the movie, apparently hitchcock was behind that decision:

"The characterization of Bates in the novel and the movie differ in some key areas. In the novel, Bates is in his mid-to-late 40s, short, overweight and homely. In the movie, he is in his mid-20s, tall, slender, and handsome. Reportedly, when working on the film, Hitchcock decided that he wanted audiences to be able to sympathize with Bates and genuinely like the character, so he made him more of a "boy next door."[12]"