Bazel is just such a nightmare for me. It's amazing when someone understands it really well and can set things up. But for anything short of that, being on the hook to fix or debug things makes it a nightmare. That and trying to port anything over from sbt, like scalafix for instance, to bazel is a pain.
Also too, bazel has this issue of googleability? like I feel like I can take any build issue I've run into in sbt and find the solution and an example by just searching, but with Bazel, anything outside of the happy path is a recipe for pain
My experience with Bazel (7 years rolling it out and maintaining it in a large company) is that it provides huge value for larger teams/codebases, but at a huge cost in complexity. e.g. the three I rollouts I was closest to each took ~2 person-decades to happen; might be easier now than it was in 2016/2017, but Bazel hasn't really gotten simpler over the years
Mill is intended to be much easier than Bazel. Most people would not use Bazel for a 1-person project, or even a 5-person project, and it only starts pencilling out once you have 50-100 engineers on the team. Mill in contrast works great for small projects and medium projects as well.
One way I'd look at it is that Mill works great for 1-500 person projects, while Bazel works great for 100-5000 person projects. There's some overlap in the middle, but fundamentally they target different kinds of users who have very different constraints and requirements
