Language fatigue and settling on C seems to be a thing, as I've encountered several people with the same opinion. I wonder what the physiology is behind it.

For me, C is the lingua franca. With C I can read kernel source, I can read systemd source, I can read firmware, boot loader, etc. I want to specialize in the language that gets me the most bang for my buck. Rust is a compelling future, but it's still the future and not the present, and the present doesn't seem to be going anywhere fast.