Rust's safety features and assurances get in the way of absolutely minimal latency requirements. It'd end up as a heaping layer of `unsafe{}` blocks, which would defeat the point, and I'm not even sure that would be sufficient. C++ lets you make a lot of unsafe assumptions about aliasing and such, which an optimizing compiler turns into extremely fast code but is in general unsafe. I'm not sure the Rust compiler would be able to output such code as it currently stands.

Rust's approach is to produce code that is as fast as possible, but with the assumption that safety is paramount over breaking speed records. That's opposite the tradeoff that cutting edge games want to make.

Keep in mind a game engine might make updates to 100,000 objects, 144 times per second. In that context, every nanosecond really does matter.

Investment banks / high frequency traders care a little bit more about safety guarantees. But not as much as you might think. A segfault can cost you a trade, but being 0.5ns slower than the competition will cost you your business.