(A) It's a form or contrarianism, in that it's an negation of mainstream preference, hence unusual. Even better, this negation of mainstream preference isn't really threatening anybody, hence good way of attracting mainstream attention.
(B) Brutalism is often associated with left-wing / communist large-scale social engineering, and the left reflexively celebrates anything done by the left. (Aside, the association of brutalism with the left is historically quite false, e.g. people like Le Corbusier didn't meet a dictator he didn't like.) So where brutalism is celebrated by somebody who's explicitly and self-consciously political, it's a Gramscian hegemonic strategy [1]. An example of such a writer is Owen Hatherley [2].
(C) Cities with a lot of brutalist architecture, prevalent in the former Soviet block, use it to market themselves are tourist destinations. This ties in with (A), for why would you go and visit a city unless it had something unusual to offer, something Instagrammable, something to talk about when you are back?