It's likely AI slop.

I made a language design some years ago. More recently, I had Claude carry out some of the implementation to see if it would work. It did not. I tried again, hand-tailoring the IRs and many of the main algorithms, and it did better but the self-hosting compiler still violates many of the design principles and even behaviors in the design document. I have spent six months of free time reviewing and fixing it myself, and it's just a small pet project. I would not open-source that code any time soon.

I must imagine Mojo is in the same situation.