Rewriting in Rust, increases the contributor pool for these project from some x to some y. Where x is the subset of people in [1, 2, 3, 4, 5] and y is the subset of people in [1, 4]:
1. Who are eager and have time to help
2. Who know manual memory management really well (also diligent enough to use that knowledge appropriately) [Made redundant by compiler]
3. Who can successfully build, link and test C code on multiple platforms [Made trivial by Cargo]
4. Have appropriate domain knowledge
5. Are not afraid to refactor "working code". [Made better through first class testing, the compiler and community mindset]
There is also the aspect that experts get a dramatic boost to their productivity, reducing their time needed, and therefore reducing the level of incentives needed.