The documentation is distributed locally, as static files, as well as being available on doc.rust-lang.org. This is considered a big feature.
I personally would love to tell people "sorry, you have to run a basic web server, even locally" for a few reasons, but it doesn't feel socially viable at the moment, sadly :/
Here's one way you might be able to make the case: If you require a web server even locally, then the docs can be installed as a single file (zip archive, SQLite database, etc.). This would eliminate the overhead of lots of small files on at least one popular desktop OS, speeding up installation and updates.
I personally would love to tell people "sorry, you have to run a basic web server, even locally" for a few reasons, but it doesn't feel socially viable at the moment, sadly :/