I can't answer for the OP, but "because we can" is a valid enough reason (pun unintended) for me.

IMO, an individual dev making a fast useful tool should always be welcomed as a feat of worthy hacking.

According to the "Purpose" section of the readme, it doesn't look like beating jq's speed was ever a goal. It was meant to be a learning exercise.

But if I had done something like that, and then serendipitously discovered that I was exceeding the original's performance, I certainly wouldn't be shy about it.

Also, this comes across as armchair criticism purely for the sake of armchair criticism. My own experience has been that, when I'm doing ETL that involves wrangling JSON, the "wrangling JSON" bit of it is almost always the bottleneck. So any improvement is more than welcome and deserves to be cheered. Even if it's an improvement on something that's already the current fastest way to do it.

I'm not sure at which "we" do you refer.

Reimplementing a piece of software that is 12 years old which mimics their UX and improves performance and error messages it's more than welcome in my opinion. My purpose was to learn the OCaml stack of writting compilers, so I personally found that I "needed" a language already created.

Thanks for raising those concerns

If we were at a board meeting deciding how to spend my time, no. If it is done? Why not

Batting practice.

We'd all be better off if plebes grew their skills by reimplementing common tools.