The Bun team is really good, and Zig is a productive language.
But there's also the simple fact that when you reimplement something, it's always going to be easier and faster than it was to write the previous implementation.
You know from day one what the baseline of the project will be, and can skip all the refactoring steps the predecessors had to do in order to implement new features. You also know what worked for them and what didn't. And what users liked and what users didn't use and ended up being code rot, so you can prioritize accordingly.
I thought the creator of Deno, Ryan Dahl, is also the creator of NodeJS. So by your reasoning, the development of Deno should go faster than Bun's, no?
But there's also the simple fact that when you reimplement something, it's always going to be easier and faster than it was to write the previous implementation.
You know from day one what the baseline of the project will be, and can skip all the refactoring steps the predecessors had to do in order to implement new features. You also know what worked for them and what didn't. And what users liked and what users didn't use and ended up being code rot, so you can prioritize accordingly.