To be fair, in a sense it's less surprising when the most notable project in Rust, from relatively early on, was a web browser.
That seems pretty uncharitable, there's more than a few OS projects happening in the Rust space and I know a bunch of people spend time poking at low-level stuff(myself included).
The above poster didn't say that there weren't any OSs or low-level stuff (anyone who frequents HN would know that) they said that majority focus is elsewhere.