You can use hugo to fetch JSON, YAML or CSV data from remote URLs and use those data as part of the build process. And if you use local data files instead of HTML you can use a tool like netlify-cms (github.com/netlify/netlify-cms) to give end users an easy way to work with that structured data without ever touching text editors or the like...
And as jacquesm said, once you have a more complex site with lots of pages, you'll want to use partials, reuse content in different places (show a summary of an article on an index page, full article inside, small blurbs on the homepage, etc), and once you get there you really don't want to write HTML by hand...