Because writing Rust backend is needlessly complex for majority of projects.
Still easier than dealing with node dependencies, webpack and co, they make me wish to write ASP with OCX components instead.
I've had a great time using Rust with Actix as the framework.
There’s a middle ground between node and rust. Dotnet and Java are wildly productive places to work but they’re not as exciting as rust.
Also, writing JavaScript for the backend is needlessly underperforming for anything with any load.