TL;DR: Just the right abstraction.

Hugo provides the right abstraction for making websites, not too abstract, not too realistic.
Writing pure HTML websites is too much work, you also need to make sure every style sheet is working on your website.
Using a content management system like WordPress is so easy, to the point that you don’t know how your website works, unless you care about it.

Hugo, like any other static site generator like Jekyll, provides a just right abstraction, not too hard like writing HTML, and not too easy to the point you don’t care about how your website works.

In static sites generators, sometimes when you need to really tweak your website, you also need to have some knowledge about HTML, unlike in CMS where “what you see is what you get.”

Well, the choice is yours, when you are driving, do you care how your car work? Do you use manual transmission instead of automatic transmission? It really depends on if you want to learn, but if you really want to learn in how your website work, use a static site generator like Hugo.