Apple came out with Swift to make iOS development easier. I think Google is trying to do the same thing by adding official support for Kotlin in Android.
People like it because it is a less bad Java. Most of the benefits with fewer drawbacks.
I personally prefer scala but the market doesn't seem to be going that way.
I'm sure they would have also developed the build language from scratch also, and I doubt it would have been as cluttered as Apache Groovy. Check out the Groovy developers mailing list [1] to see how inactive Groovy development is nowadays.
[1] http://mail-archives.apache.org/mod_mbox/groovy-dev/201705.m...