It's because of the compiler and SBT to be frank. They are very very clunky.
See https://scala-ci.typesafe.com/grafana/dashboard/db/scala-ben...
Also SBT has been much less of a nuisance recently. They've made quite some effort to get rid of the most obscure syntax and with the recent improvements in compiler speed it's inching to 'acceptable' territory.
I admit that I really love the language, though.
I seldom see conference talks how to optimize Maven builds, Gradle talks about build optimization, at least one per Java conference, and several per Android one.
Just Google IO 2019 had three talks about it.
I've never had a gradle build that didn't manage to remember I've only just compiled the code and haven't changed any of it. I can't remember ever having a maven build that could tell I didn't need to compile every single time. And the same the whole of the way down the stack.
Nice attempt to imply gradle isn't declarative though.
Again just Google IO 2019 has three talks about tackling build performance issues.
Maven never required a build performance profiler tool.
Gradle is just like Ant, give DevOps a programming language DSL and they will make a mess of build scripts.