Agreed. If somebody doesn't know Java and decides to jump to Kotlin, I will have the same question: why not Scala which is used more than Kotlin on computers (i.e. non-Android)?
I'm not necessarily advocating for Kotlin but the key argument would be supportability. Scala is a very complex language+ecosystem with idioms many people are highly unfamiliar with. Comparatively, Kotlin can be written idiomatically in a way that the vast majority of developers will readily understand and quickly come up to speed with.