Yes, some people who previously used Scala, now use Kotlin. And some people who would've used Scala if Kotlin didn't exist, use Kotlin. Same probably goes for Rust.
But there is a big enough market for people that like the intricate and expressive type system that Scala gives you, in combination with the JVM ecosystem. People that think Kotlin is nice, but not expressive enough, for example. People who don't want to deal with Rust's memory management and/or don't have a use for that. People who think Go's simplicity is sometimes more of a burden.
Why are people so intent to bash sombody else's language choices?! Go, Rust, Kotlin, Scala are all great languages in different ways. They all cater to different needs, sometimes radically different (Go vs Scala), sometimes subtly different (Kotlin vs Scala). I think there is a market for all of them, and more. And the introduction of a new language (Kotlin for example) does not necessarily spell doom for another (Scala).
Let's all enjoy our own tastes and needs, and respect those of others.