Most code is not CPU-bound, and for code that is, a hot spot is all the usually needs to be optimized. Today .Net Core is remarkably performant, and the fact that just by writing code carefully, or using Span<> etc., you can get close to bare-metal perf with w/o resorting to FFI to unsafe code is a good thing. This is much easier than trying to keep your friendly Rust borrow-checker happy even for moderately complex data-structures with varying lifetimes.