Zig has some advantages for such projects, especially in the beginning.

Among them:

- much easier to iterate on (due to the language being simpler and compilation much faster)

- native C/C++ interops (Zig can compile C and C++ and mix it with Zig) which is crucial for a node-replacement runtime that runs an open source JS engine

- fewer dependencies and trivial static linking

I guess that now that they've been acquired by Anthropic there's this combination of having both in-house Rust talent, AI which does better on Rust, and the funding and resources necessary to undertake such a migration.