Difficulties arise as your site becomes larger and more complex. Consider navigation: it may be similar in every file, but adding a new page requires updates to every other. Even references to CSS and images can become awkward as folder structures evolve.
Consider collaborations: coordinating continuous integration from multiple sources or departments, needing the liberty to independently modify their portion of a site.
I propose the use of HUGO – a Static Site Generator.  An SSG is a compromise between using a hand-coded static site and a full CMS, while retaining the benefits of both. In essence, you generate a static HTML-only website using CMS-like concepts such as templates. The content can them be extracted from Markdown files.