Another thing is that having large-scale successful projects make Rust a more likely language for other people to choose when creating a new project themsleves.
"It's a neat language, but no one has used it to make anything that isn't a toy" is a really common mindset for the people who make such decisions.
The only way to change that mindset is for the evangelists to write software and show that yes, it is possible to write For Realsies software in that language. If that happens to be a rewrite of a successful project, fine - it's still a large project, and it'll inspire more development than someone coming out of nowhere with a project.