Why is the class sold in Scala?

Why isn't scala.collection.mutable.TreeMap sold and other Map (for example, HashMap)?(Furthermore, the immutable TreeMap was final, and HashMap was sold, so no modifier criteria could be found.)

I thought the reason why I use the sealed class in Scala is to combine it with the case class so that the compiler can detect pattern match leaks, but is there any other reason?

scala

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