Because Scala allowed you to write much less code than Java. After Java was bought by Oracle, they shifted to a faster release cadence and new features. But developers still had to use things like Lombok, Guava, and Apache Commons to have an easier way to do things.
Now, both Kotlin and Java 25 have a lot of the features that Scala was the first to introduce, so it does not seem important. But it was very important back then.
Also, the Big Data world was embracing Scala. Apache Spark is written in Scala and so many other important tools and libraries in the Big Data ecosystem were in Scala.
Edit. Fixed information about releases after Oracle acquisition.