People wouldn't care much for Rust at all if it didn't offer two things that are an absolute killer feature (that OCaml does not have):
* no GC, while being memory safe.
* high performance on par with C while offering no-cost high level conveniences.
There's no other language to this day that offers anything like that. Rust really is unique in this area, as far as I know.
The fact that it also has a very good package manager and was initially backed by a big, trusted company, Mozzila, while OCaml comes from a Research Lab, also makes this particular race a no-brainer unless you're into Functional Programming (which has never been very popular, no matter the language).