@pete_wright this is not really specific to Rust but of most modern development in general.
Ironically, Rust actually makes it easier than ever (IMHO) to write cross platform code. While FreeBSD isn’t a common target, it’s not hard to make most crates work on FreeBSD, but it seems there just isn’t the effort to pay attention to BSD differences vs Linux.
Which is very sad as I’m a huge fan and daily user of both Rust and FreeBSD.