Some of the newer material libraries are kotlin only. It does seem to be happening.
Kotlin can't be called from Java land?
It can.
Jetpack Compose cannot be written in Java because it relies on a Kotlin compiler plugin to transform composable functions.
With some limitations. Mostly writing Kotlin code that is a used friendly enough for Java developers requires a bit of extra effort. It's not something that a lot of Kotlin developers waste time on.