s/suffered/enjoyed/
A rewrite usually improves a lot of small things that were found in the previous version. It's like a new major version, even if it does not add new major features.
It's an expensive undertaking, though.
Thanks, if you watch the Fuchsia tour session, they hint at some of the rewriting taking place.
They are now starting to rewrite OS components in Rust, and I wouldn't be surprised if that happens to Zircon as well, it stared as a C anyway, and thus already suffered one rewrite.