If I want to call ruff, I can do so myself. Why should I want to call it through uv?

If you want to call ruff directly, this doesn't change anything. It's a purely optional feature.

However, to answer the question generally: people want this for the same reason that most people call `cargo fmt` instead of running rustfmt[1] directly: it's a better developer experience, particularly if you don't already think of code formatting as an XY-type problem ("I want to format my code, and now I have to discover a formatter" versus "I want to format my code, and my tool already has that").

[1]: https://github.com/rust-lang/rustfmt

Some of us prefer well packaged tool that does everything instead of stitching together bazillions of dependencies.