I'm pretty sure the number of programmers who know C is several orders of magnitude higher than Rust.
You don't get it. In every respectably-sized C project, there are lots of assumptions about "objects" lifecycles (who allocates, who has to free), concurrency access, etc. Unless you have spent a long time in the code it's difficult to know all the conventions used throughout the project, and you're pretty sure you'll shoot yourself in the foot the first time you'll try to modify the code.
In Rust, all these conventions are encoded in the type system and are checked by the compiler. Which means that when your modification compiles, it already respects these conventions and you're pretty sure it won't break one of those subtle assumptions. At least not so easily than in C. So your patches are easier to review. So the barrier to entry is generally lower.