to survive startup, you need a large pool of talents, mature and verified and boring stack, easy to find tutorials, etc. The least thing you want is to spend cycles on fancy new bleeding unstable languages to build your earth shaking product.
Forgive me if I'm quoting you out of context but the article mentions receiving 4000 applicants over 8 weeks time. I've hired (primarily) for Java and DBA positions, and we would be absolutely thrilled if we got even 40 applicants.
Many people are searching for Rust jobs, but few have a really strong experience with it.
You could just filter the CVs for Rust experience and then take the most impressive 10 or 100 to interview.
Where does a language magically go from "new bleeding unstable" to something you think is suitable to use at a startup ? Rust 1.0 was in 2015, seven years ago.
Do you think a startup should also avoid the "fancy new" ES6 with "let" and arrow functions ?
They all miss their 5 million LoC mudball at the bank, because that's all they know how to do.