Java is a simple language, the syntax is easy to parse and logic is generally straightforward to reason about - as a programmer you have very little ability break expectations of how the language itself behaves (no operator overloading, etc).
Scala, on the other hand, gives you a huge toolbox down to some really complicated to reason about features like implicit parameters, creation of completely arbitrary operators, etc.
[Insert some funny pun here about Java giving you a simple tool while Scala gives you an incredibly complicated one]. They're both great languages, but they serve very different purposes and audiences - Kotlin happens to fit Java's demographic better than Scala as a result, it doesn't have the magic and complexity to the same degree Scala does (the most confusing new constructs probably revolve around builders/lambda's with receiver types which aren't needed by most developers not writing DSL's).
