It is well supported by the project itself, we offer a variety of tools so that you do not need internet access, and this was also a hard requirement of a lot of our early important users, like Firefox and various distros.

Even with using crates from crates.io.

If crates.io was down tomorrow there would be a major disruption to you if you were using Rust for development. That is their point, as well as potentially exploring other reasons.

As someone who uses a source-based distro I hate language package managers. They always end up inferior to a distro package manager and create extra work for everyone, including the language developers, who tolerate it because it is in their favorite language.

It would only be an issue if I wanted to use crates that weren’t in my local cache already. And that’s gonna be true of any build system. It would also be true of any distro package manager.

Most other software is more dispersed and has plenty of mirrors, e.g. the Debian project. The same criticism of crates.io is typically levied against GitHub.