Kotlin's adoption is not that much bigger than Scala, and it's no good to me, as it's heavily concentrated in the Android world, which is irrelevant to me. Among other things, that means that Kotlin.js is not as good as Scala.js, both itself and in terms of the ecosystem – and the quality of Scala.js is half the reason I'm using Scala in the first place.

Kotlin as a language is also closer to Java on the Haskell <---> Scala <---> Java spectrum. We just don't want to move in either direction on that spectrum, Scala sits perfectly where it makes sense to us.

It's interesting that some people here are saying that Java's recent improvements will eat into Scala's market, when actually, it seems that it will eat into Kotlin first.