I imagine it's about type signatures. Rust makes it very easy to attach strong invariants to types. In most other languages, it's either harder to attach these

I imagine it's about type signatures. Rust makes it very easy to attach strong invariants to types. In most other languages, it's either harder to attach these invariants or harder to trust them. By one metric (definitely not all of them), this makes properly written Rust code much easier to understand (and trust) than in the other languages from that list.