Google lets Android Java stagnate on purpose on Java 8 subset, with cherry picked APIs from newer OpenJDK versions, uses this language subset to sell Kotlin features over Java features on code samples comparisasions.
Nowadays, all Android developer channels, regardless on which form, are all inundated with Kotlin material and how great it is over "Java" (actually Android Java).
As for JVM being flexible enough to support Kotlin, doesn't seem to be appreciated by the Kotlin community that spits on the hand that has made the language possible to exist in first place.
Language wars don't have a place when languages share the same platform, as such I have zero tolerance for communities that cargo cult otherwise.
When Kotlin is so great and doesn't need Java for anything, they should port everything into Kotlin/Native and succeed on its own merits.
I also find language politics to be incredibly boring. Maybe you have a point, but I just want to write code in a language that isn’t 10 years out of date.
For better or worse, Kotlin designers have decided to make a deal with Android for turning it into Kotlin's plaform, and they definitely do not care what happens with the JVM.
Kotlin designers will eventually, like everyone else, find out that one cannot stand on both sides when things start heating up.
Then there is the whole matter of ChromeOS vs Android vs Fuchsia of Google's internal politics, and Kotlin is only relevant in one of them.
As for the Android Runtime, Android team is gatekeeping Android Java on Java 8 subset on purpose, as means to serve their political games to push Kotlin no matter what.
Kotlin without godfather Google will just fade away.