100% Pure Java is because Java is actually about four things. One of those things is a Virtual Machine, which means you don't give a shit that the implementer has never seen an ARM CPU, because you've got the Java VM, and so their code works fine on your ARM CPU.

But if their "Java" software is actually 10% i686 Machine Code then that won't run on your ARM CPU, you will need to undertake an expensive port or move to Intel. So hence 100% Pure Java == Write Once / Run Anywhere actually delivered.

You can argue that Rust is more than one thing, but certainly not to same extent. Rust's culture is crucial to its "A language empowering everyone..." slogan, but it's not really separate from the programming language, in the way that the Java Virtual Machine doesn't need the Java programming language or the Java security model (now obsolete) or the Java browser plugin (remember that?) and so on.