Brutalist architecture was a disaster, especially in countries like the UK where poor light and regular rain make grey concrete one of the most depressing and least durable of all possible building materials.
The UK was littered with Brutalist "statement" buildings. Most have been pulled down now, and - with a few high profile exceptions, which have escaped the low-budget ghetto most of the movement settled in - the style is generally considered a mistake.
I have no idea why anyone would want to copy the aesthetic in web design. But then the designs on show don't look Brutalist so much as "edgy" 80s magazine kitsch, which in turn influenced a certain kind of minimal web style which has actually been around since the 90s.
It's true that web design lacks real creativity and diversity, but that's partly because web pages that are trying to sell you something - as opposed to making an artistic statement - are optimised to balance content delivery with behaviour modification with cognitive load. There are only so many ways to do that, and the affordable ones are already in use.