For me the alternative to Crates.io/npm/PyPi is a "platform release" like Android where a bunch of stuff is signed off by a corporation.
Whereas the developer of a popular Rust library most likely just added some dependencies that were convenient, and doesn't know the full story of the transitive dependencies.
To me it is much more likely that somebody at Debian _saw_ the dependency being shipped than an arbitrary Rust developer, who probably does not even know how many dependencies are being shipped with their program.
DDs review the libraries they package. All uploads are personally signed to keep people accountable.
Instead opening a github account and developing a library can be done anonymously and there's been supply chain attacks done this way.
All this is to say: a large amount of debian users likely are using rust, and an even larger amount of non-debian users is likely to be using rust.
those few narrow components likely have good support.