I mean sure sometimes it is but show me a Rust software that didn't advertise itself being written in Rust.
I also dislike the emphasise on the programming language, but many people seem to find it important.
Presumably because I'm going to be writing the same language when I interface with it. Rust can export to a C API but if I'm using Rust myself the API is going to be better.
There are enough existing and new game engines and frameworks that if the title was simply “Bevy: A Game Engine”, then I might not have bothered to clicked on it only to find that it was written in C++ or Lua or Python or what have you. I use other languages too, mind you, it’s not that – it’s just that aside from Unreal, Unity and Godot, the only other game engine or framework that I am interested in knowing about at the moment is one that is written either in Swift or in Rust.
Conversely, stating it upfront also allows anyone that does not want to write in Rust to avoid this particular game engine at the moment.
I see only benefits of stating it.