I think that early web (say, pre-Web 2.0) was the epitome of Brutalist design. Because resources were limited, you had to make the most of what you had, leading to that no-nonsense, sparse style. I think it's beautiful, in its own way.
That rawness, without too many attribute tags let alone CSS, is brutalist.
For instance, if a site didn't have a proper search function, but had a pretty logical URL scheme, you could often find what you need by trying a few permutations in the address bar. The limitations of the system meant web "designers" (I'm using that term loosely) had to build fairly organized and unintentionally "Brutalist" sites if they wanted to be used by any large number of people.
Hope that made sense, I'm still waiting for my coffee to kick in.