You are asking a question that doesn’t make sense. It seems like to you it does, and to others it sounds like “what does the color blue taste like?” People do stuff for fun. It doesn’t have to be useful. Or it can be useful to them because it isn’t the existing thing. xv6 is great, this is different. It makes different choices and studying the differences can be a good thing. Comparing two different pieces of software written in the same language is sometimes exactly what you want.

The logic of “something similar already exists so don’t bother” is reductive. I am sure 99% of hobbyist software is useless to anyone but the person who wrote it. It still helps people learn and become professionals.

Remember a few weeks ago there was a post here by a high school student detailing building a laptop from scratch. Was that wasted effort because you can just buy a laptop? Was Linux wasted effort? Why does this project offend you so much that you keep commenting on it in such a negative way?