Scala was sold through Akka and Spark, solving pretty complex technical challenges that are less relevant nowadays. In fact if you can avoid Akka and Spark, do.
A lot of companies followed the hype without investing in the developer experience. Tech debt hurts more in Scala than in a bigger, slow moving language. After typical turnover, you get teams inheriting unmaintainable codebases. This leaves a bad impression. It can be avoided, Twitter built world-class SOA with Finagle, as well as a complete layer of libraries on top of Hadoop, at a time where the Scala ecosystem was even rougher.
The fact Databricks doesn't care much about the language also did tremendous damage, forcing the community to cross-build against very outdated versions of Scala.
In short, Scala was never a better Java and adopters who thought otherwise invariably got burned.