Why Kotlin when you got Swift is an equally valid point. People like choice and for a lot of us, running on the JVM is a non starter.

Try creating a small command line tool for a JVM language. You need to distribute a virtual machine with it. You got the overhead of firing up a VM or JIT just for a short lived session.

Also JVM gobbles memory. You would not want a system made up of lots of tiny command line tools all running on a JVM. That would be a lot of overhead.