If the goal were to generate pages from a document DSL like Markdown I'd understand the need for a transpiler. But here the author's done it to make the HTML "look cleaner".
Boilerplate is barely reduced, it's mostly been replaced with different symbols and words. Now instead of some extra characters, you've got an additional build step and a new suite of tokens to learn.
And sure that code looks "clean", but it's much less clear than the original source would be. Whitespace is syntax, the delineation between tag & content is much less clear, you can no longer see where tags end without carefully following the indentation or using editor highlights. Then you've got HTML & CSS semantics in a YAML-but-not-quite presentation with both CoffeeScript (javascript-but-not-quite) AND Python, all right next to each other, with the only separation at the bottom end being a line break.
I just fundamentally don't understand it. I suppose it's not aimed at me.