Because it's written in Rust.

Seriously, though; there are a dozen widely used make systems, most of which are more widely used than just. People have ideas and think they can improve. As far as it goes, having a bunch of different make options is one of the least annoying areas; diversity is mostly hidden from end users, and you only really have to learn it if you plan on becoming a contributor.

However, if you're asking for a comparison table, a "why is this better than make, or ant, or maven, or cmake, or ninja, or just, or rake," then yeah, I agree. Having a brief elevator pitch is appreciated.

Your comment is perhaps a bit confusing without a link: https://just.systems/man/en/