Why would I want to use this over, say, Node.js and TypeScript?

I believe if the work you do fits well with Node & TS, you have no reason to use zig (other than for learning or curiosity). Like, if you don't need every drop of performance, memory layout & control, there's more downsides to using zig. Idk, cruds or "enterprise" stuff or websites don't benefit from zig.

I suggest you try using Ghostty (written in Zig) for a bit and compare it to another terminal like Hyper (written in JavaScript).