I think this is the case with most JVM languages, to be honest. As someone who has done some Java but would never do it willingly as part of a hobby project or

I think this is the case with most JVM languages, to be honest. As someone who has done some Java but would never do it willingly as part of a hobby project or the like I think Kotlin and pretty much every other JVM language is a huge step up from Java. When you're already knee deep in it I suppose you're bound to have a less enticing reason to use the other languages. That being said, I don't see how you can look at the feature list of Kotlin and play around with it without seeing how it's obviously a much better language.