Inertia. There are still a ton of Java shops out there, and many of them will not switch even partially to another language anytime soon. The hope is that these orgs might find it easier to upgrade to Java 21+ than to learn and start using Kotlin/Scala/etc. I fully expect I might find myself working at such an org again, and when I do I’ll be grateful for newer Java features.

Signed, a dev who would never willingly choose Java over Kotlin for anything ever again.