Scala was designed as an experimental language, and it succeeded beyond that initial purpose. Kotlin is the language that many people wanted but Scala almost was.

Scala continutes to be an experimental language, pushing ideas that aren't ready for the mainstream, such as having an internal representation that is as rich as the original code.

Meanwhile Kotlin is adding practical features for which Scala has no equivalent, such as async/await. It's concerning that Scala has had a proposal on the table for years and haven't touched it—despite the huge amount of use it gets in C#, JavaScript, Python, and Kotlin. Especially since reactive applications are Scala's main real-world niche.