Because I got tired of seeing creators squander opportunities by failing to communicate why their product is any good.
I created the blog Your Landing Page Sucks! to deal with that, and the Landing Page Cookbook is the book-format, way-more-actionable version of the blog.
It condenses the most important insights about all aspects of landing pages, and gives you the best building blocks to accelerate the landing page creation process.
Sorry, but I'm a bit selfish — I also created the book for myself and use it constantly when creating new landing pages.