It's amazing how many people in this thread justify their own language choices by making negative, sweeping statements about another language (Scala in this case) that is successfully used by people other than themselves. 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…
Partially it's simple tribalism. But part of it is also the rational awareness of the opportunity cost of investing in a language other than the author's preferred one. The more people using language X that I don't like, the fewer people using my preferred language Y. That means fewer libraries I can use, docs I can read, bugs that get fixed, etc.
Language ecosystems aren't entirely zero-sum, but they aren't totally orthogonal either.