Honestly I feel like if Scala would pick a less insane build tool, it would have much better adoption.
I've used the build tools of almost all the major languages (JS/TS, Rust, Haskell, Kotlin, C etc) and I don't honestly see any which are particularly easy.
I would definitely agree with your point that most build tools aren't easy! I've used maven and grumbled about it, and I'm mostly sold on scripting my build in the same language I'm using anyway, but in my long time on the JVM, it's always been the gradle and sbt projects that end up with inscrutable and hard-to-follow build scripts.
The sbt REPL also regularly breaks existing build scripts by changing how args are passed/parsed, or even how terminal color support works, and I just get sad every time I see a new, unexpected error from one of our CI runs.
Take for example the point on syntax - is gradles groovy receiver syntax not just as esoteric as operator overloading?
My question was what makes SBT uniquely bad when the topic of build tooling comes up that people immediately comment how terrible it is.
I even went to a lot of effort to master SBT. I've read through the official docs numerous times, and Josh Suereth's Book https://www.manning.com/books/sbt-in-action, and I still feel like I don't grasp it very well. I'm just not smart enough for SBT.