More (many more?) of us are familiar with and have familial connections with the Mediterranean. We also have easier access to, say, olive oil than pickled plums.
Remember, the goal of marketing a diet is selling books. Books telling you to find, prepare and eat seaweed are a harder sell than books telling you to eat ingredients you're probably already cooking with (but maybe in different quantities) and use tools and techniques you're already familiar with.
Also we have a much longer tradition of western European cooking on a pedestal. Asian recipes really only start showing up in American media in the 90s, and blew up in a serious way in the 2010s.
Japan in particular is not food self sufficient and has a declining agricultural production so is not spending as much money on convincing people to export food. Plus technically a lot of Japanese food is not grown or caught in Japan and so can be made elsewhere using the same recipes.