People can have various reasons for such look. It can be a symbol of non-conformity.
Official Rust spaces have a code of conduct that is inclusive and forbids discrimination, and this may attract people who otherwise wouldn’t feel comfortable to participate.
To generate the LLVM code correctly you need to run build.rs if there is any, and run proc macros which are natively compiled compiler plugins, currently running without any sandbox.
The final code isn’t run, but the build process of Cargo crates can involve running of arbitrary code.
The compilation process can be sandboxed as a whole, but if it runs arbitrary code, a malicious crate could take over the build process and falsify the LLVM output.
Plus you can make certain sites always automatically open in their designated container, even if you followed a link. You can keep sites know for spying away from your logged in identity. You can have your banking and other important sites in another container for extra defense in depth.
I maintain a long-term Rust + Node.js project, and the Node side is the painful one.
Node makes backwards-incompatible changes, and doesn’t have anything like the editions to keep old packages working. I can end up with some dependencies working only up to Node vX, and some other deps needing at least Node v(X+1).