Java nowadays is mostly used for business applications, where developer productivity is more important than runtime performance. Java being memory safe is a huge part of that, which is the JVM platform. Java the language had the major feature of being superficially similar to C++, that helped take over the business market but is now no longer relevant. When Java was first marketed as a business application language there were few competitors. Nowadays there are, but nowadays the major reason to choose Java is because it is entrenched and good enough.
However all the Java shops I hear about are also looking into Kotlin at some level of adoption. From all the new JVM languages Kotlin integrates the best with the existing Java environment and for displacing a language in an existing niche an easy upgrade path is the most important. So I think Kotlin will become an important language in the JVM ecosystem, it will just take a long time because these types of businesses are conservative in their tech choices.
While Google's support was definitely a factor, Go also had some important language features going for it. Most importantly it is targeting a relatively empty niche in the programming language landscape, i.e. that of high performance, close to the metal languages with little performance overhead, while still being easy to write. "Easy to write" for 80% comes down to being memory-safe, unlike C/C++. If you're in that niche, you have few alternatives. The other options for mainstream memory-safe languages are interpreted scripting languages and Java-style jitted languages. Go easily beats both in resource consumption without being much harder to program in. Rust isn't really comparable because while it is memory-safe its memory management system still forces the programmer to think about the memory and resource usage, thus being slower to program in.
Rails was the first of that type of web framework. Django and all similar frameworks are Rails clones. At that time Rails was the killer app for Ruby. Unfortunately for Ruby the other languages were willing to put in the effort to copy it, and Rails is no longer a unique advantage.
However all the Java shops I hear about are also looking into Kotlin at some level of adoption. From all the new JVM languages Kotlin integrates the best with the existing Java environment and for displacing a language in an existing niche an easy upgrade path is the most important. So I think Kotlin will become an important language in the JVM ecosystem, it will just take a long time because these types of businesses are conservative in their tech choices.