Most of these websites are a rebellion from the predominance of the Bootstrap UI, with its clean, responsive designs, and to the more and more senseless diktats that digital media had to abide by in order to make a profit in the early-to-mid 2010.

Websites look coherent even if they don't have "clean" UIs.

[Brutalism] is kind of taking everything that you don’t see on the internet that you still see in print or vintage design, if you will, even kind of a nod to the past, blowing it up and bringing it back on the web,” said Blake. [...]

This experimentation comes from seeing the internet as a medium for making (and not just showcasing) art.