Jujutsu is built on top of Git, so it can benefit tools in the same ecosystem (forges, CIs, code quality tools, IDEs, plugins, etc).

I have only played a little with jj and hg, but I felt that jj has a more modern UX, learning from years of Git existence (and even influencing Git, like the new `git history` command [1]). On the other hand, hg was created in the same month as Git, both trying to improve the experience of the VCSs available at the time (april 2005).

[1] https://lore.kernel.org/git/20250819-b4-pks-history-builtin-...

Others have answered about traction. As a one-time Mercurial user, I think the single most significant addition is first-class conflicts, so that dealing with them doesn't stop the world but can be deferred until I'm working on a particular conflicted change. (That also eliminates the need to ‘evolve’.) Easy undo is also nice.

Git already won through Github, the Linux kernel, and other important projects. Even if you like Mercurial's syntax better (I do) and wish it won (I do), that battle was over many years ago.

jj's data store is git. You can use jj while other people on your project just use git. There's no migration of data or history. You can use Github and all of the various git tooling that exists today.

As such, the initial cost of switching to jj is zero for individuals, teams, or projects. That's huge.

jj's ergonomics are significantly nicer. Fewer ways to shoot yourself in the foot, much better merge resolution, etc.

Mercurial is too slow. Even with chg common commands like `hg status` may take hundreds of milliseconds. JJ is fast. Internally `jj log` taking more than 500ms is tracked as bugs.

> And why would it get more traction than Mercurial?

There's no network effect headwinds, it's interoperable with git (I assume most people using jj have an upstream repo that's on git).

My relatively ignorant take is that it's pretty similar to Mercurial, except that it's compatible with git repos, which is also the answer to why it might get more traction. At least from my standpoint, it also doesn't need to get traction, because I freely use it with git repos without any of my coworkers needing to use it as well (although they might! I have no idea, just like they probably don't know I use it)