It's not a rust specific thing at all, HN has had it's share of “<something> but written in JavaScript” (as well as in Go[1]) back in the day, it's just a common thing when a language becomes popular, as their are more people wanting to show off that they did something than people with genuinely original ideas worth posting on HN.

It's not that Rust or Go aren't used to write new things, it's just that the bar for reaching the HN front page with new things is much higher than for mere copycats.

[1]: https://hn.algolia.com/?q=written+in+Go