Because landing pages are a single page they only require the one index template.
/templates/index.liquid
The site themes control everything from login to the customers product library. There are many pages that make up a fully functioning site theme.
/templates/404.liquid/templates/blog.liquid/templates/blog_post.liquid/templates/blog_search.liquid/templates/forgot_password.liquid/templates/forgot_password_edit.liquid/templates/index.liquid/templates/library.liquid/templates/login.liquid/templates/page.liquid/templates/thank_you.liquid
A product theme is the way a user consumes the digital content.
/templates/announcements.liquid/templates/categories.liquid/templates/category.liquid/templates/comment.liquid/templates/post.liquid/templates/product.liquid/templates/search.liquid