While I agree with the basic idea, it seems that in practice it's been taken over by ascetes who throw the baby out with the bath water and impose pointless restrictions on themselves just for signalling.

If you want software to have less complexity, you don't choose a language which gives you options, you choose one which removes ways to make mistakes. That means, emphatically, not C. You don't have to choose Rust, which is complex indeed, but allows your code to be less difficult. If you want strictness, choose Haskell. Or maybe go the middle way and do OCaml. Or maybe Ada.

I don't understand how the suckless community goes from "vulnerabilities are commonplace" and calling out masterminds to writing C, which is famously difficult to code without stepping into undefined behaviour.

Or maybe I do: this checks out if minimalism is more important than vulnerabilities and simplicity.

Similar criticism can be applied to sticking to X11 compared to Wayland, regarding vulnerabilities (any application can see any other) and performance (any application can block the entire server - try ssh -X on a high latency connection to see).