Compared to Jekyll (Hakyll's obvious namesake), it seems to take what is a remarkably simple system (ie. one that puts your focus mostly on the HTML, CSS and JS and does all the hard work for you), and replaces it with something that you need to spend time actually learning to be able to even compile.

While Jekyll offers convention over configuration, this seems to go the other way. For a static website I'd rather focus on the HTML and CSS than a DSL that compiles it in a certain way.