I think it's not just that Groovy and Scala were temporarily a better Java that was eventually overtaken by the next even better Java, I think they were not sufficiently better. Better at some things, but with a cost not everybody wanted to pay. Groovy doesn't perform the way Java does, Scala is fast, but is a lot more complex and occasionally hard to read.

I haven't really tried Kotlin yet, but my impression is that it improves a lot on Java without any real downsides. It might not have all the improvements that Groovy and Scala offer, but it has the most important ones.

And it's a clean slate that leaves some of the poorer decisions in Java behind it.