Well, for a lot of people those things are enough to go back to Java and avoid having to rely on the Kotlin ecosystem (which is not free of problems).

At which point would you say Java has improved enough to catch up with Kotlin (supposing Kotlin does not also keep improving)? As a long-term user of Kotlin, I would say I would not reach out for Kotlin anymore for new projects. The last remaining big thing Kotlin gives is non-nullability, but with simple tools, Java also has that already.

I wouldn't reach for Kotlin for backend projects at all tbeh, since the ecosystem on that side is (relative to Java) immature and doesn't always play well with standard Java tools such as JPA. Non-standard tools are half-baked, inconsistently maintained and not ready for primetime. But for apps, like in mobile, the ecosystem is rich and I would prefer it over Java, especially with advances such as KMM and KotlinJS.

My point being, Kotlin vs Java isn't just about language features, it's about community, ecosystem, use cases etc.

(Fwiw, personally I prefer Kotlin because it's more expression oriented than Java.)