It's a real mystery. Some popular conspiracy theories:

* Scala projects the Haskell-on-the-JVM image too much to scare off the practically-minded. It has no ORCL or GOOG behind it (its cousin F# has had official MSFT support for a decade at least).

* Kotlin is strongly associated with the frontend. Just try to search for a backend Kotlin role in the Bay Area to see.

* Java 17-21 is catching up with Kotlin fast enough to make many people doubt the upskilling effort.