Most people don't write a basic compiler for C either, "relatively simple" or no. Most people would rather add a new target to an existing compiler, which is much easier.

It's also "relatively easy" to add a new backend to Rust.

There's a policy document for Rust here: https://doc.rust-lang.org/rustc/target-tier-policy.html

There are a lot of things that can go wrong. You want to be able to test. Being able to test requires that someone has test hardware.