Due to the success of build tools like Gradle, build.rs or any other one that packages a Turing complete language to steer a build, apparently many want such daemons on their homedir.
Just because you can do something, doesn't mean you should. A `build.rs` is supposed to be for compiling non-Rust code and stuff like that, not mucking about with the package manager – and by and large, people don't use it for mucking about with the package manager.