IMO that's mostly because Kotlin doesn't need a lot of hype to be useful.
The software industry has suffered a lot from the ecosystem problem - before the JVM started to generalise, languages were not compatible with anything except C APIs and they all rolled their own toolchains, compilers, libraries and sometimes even their own IDEs. This is such a huge pile of work that everyone subconsciously understood that it was vital to join the biggest club and try to grow your club in any way possible, as only by attracting a critical mass of developers would you get the productivity boosting libraries and tools you so badly needed.
No wonder that programming language debates often have flavours of a holy war.
The JVM and .NET CLR has helped a lot to reduce this problem because now lots of quite different languages can share powerful compilers, runtimes, access Java libraries and sometimes each others libraries, and so on. You don’t tend to see Clojure vs Scala holy wars to anything like the same extent because hey, if we disagree so what? We can still share code with only a tiny fraction of the effort it once took.
Still, there is some friction. These libraries do their own collections and the interop isn’t perfect.
Kotlin is the natural extension of this trend - it focuses heavily on Java interop to the extent that the notion of a “Kotlin library” hardly makes sense: such a thing would be basically the same as a Java library, except written in a different language. If Kotlin auto-converted Bean properties into Kotlin properties the distinction would get even thinner.
What’s more JetBrains appear heavily committed to Kotlin and are using it for their own internal codebases, so there is not much chance they will abandon it because it didn’t get huge immediately - they need to maintain it if only to develop their own products.
So why bother trying to create lots of attention and hype? The utility of Kotlin is independent of the size of its developer base to a far, far greater extent than previous languages, and that’s a good thing. More Kotlin developers might mean a handful of little libraries and DSLs that add syntax sugar on top of the real Java meat … but that’s about it.