It's its own beast to maintain. A lot is hiding behind your "just".
If the use case is single user wiki and the user is technical enough, MediaWiki requires more resources and is also more work than Git + Markdown + a static site generator if you are already comfortable with static site generators. No specific web server config, no tricky configuration files, no database to maintain, not difficulties to upgrade the server…
Now, one could argue that "single user wiki" just means "regular website" because the essence of the wiki is gone. Wiki means "quick" (friction-less?) edits by multiple users, possibly anonymous [1]). What the author of the post did is convenient handling of internal links. Which is still a good idea, but I would do it differently: I would not create a <a href="..."> tag for missing pages, that not very nice to users. If you do this, you are intentionally creating broken links that can only be distinguished with styling, which is not very accessible. Red links are useful in an actual wiki where users can actually create the page, but on a regular website, I'd use something like <span class="missing" title="Dedicated page coming"> or so (+ whatever is needed for the title text to be accessible).
