Software security matters, in the abstract, but trading firms don't care about it nearly as much as tech companies do. The other thing is that being as fast as C++ is not compelling enough a reason to replace C++ for their use cases. If anything, Rust's dependency management story would be the thing to highlight (this is part of what's compelling about the JVM).
I think the responder's version of 'safety' really boils down to 'null pointer safety' - not 'software security'.
And even then, people keep talking about it like it's 'the thing'.
Java has null 'references' as do most languages frankly and it's just 'a thing' almost never 'the thing' to be concerned about.
'What devs want' is basically something kind of like Java, but that compiles, predictable/controllable performance and memory management i.e. no GC. That's it. It will probably end up being Rust, but that's because Rust will eventually provide all the nice, clean, modern package management, idioms, libraries etc., not specifically because of the 'safety'.
Granted I don't want to diminish that in the attempt to create 'proper memory management' you probably end up writing better software anyhow.
That being said: Jane Street is pretty avant garde in this respect. I expect there already is, or soon will be, a successful trading firm which likewise builds its tech brand on Rust and alternatives to Rust standard library primitives. But overall adoption will probably continue to be anemic.
If you're interested, check out https://www.youtube.com/watch?v=10gSoVZ5yXY for an example of the types of compile time guarantees can be had.
I am aware that dependent types exist, but quite frankly I've yet to see a popular/ergonomic language implement them. As much as we'd like absence of null pointers, error types, and immutability to be the norm it is not and it will take decades until it is.