Oh well, thought Jane, that's how men are. He's probably taking it for granted. She found it very pleasant to be taken for granted by Stan
Jane reflects on men's behavior, thinking, "Oh well, that's how men are," implying a resigned acceptance of typical male actions or attitudes. She seems to recognize that Stan, her companion, might be taking her for granted, which she finds somewhat pleasant rather than upsetting.
Despite feeling that Stan might overlook her, Jane enjoys the familiarity and ease that comes with being taken for granted. Her attitude indicates a level of comfort and contentment in their relationship, aligning with the casual tone of Beverly Cleary's story in Fifteen.