What purpose does a concrete method in Java 8 interface serve? [duplicate]

This question already has an answer here:

• What is the “default” implementation of method defined in an Interface? 3 answers

One is definitely if you have multiple interfaces implemented then you can have all those methods implemented in the class.

But this could be done earlier as well with a mixture of abstract class and interface.

Then why is this done in Java 8?

Is it not against the very definition of "Java does not support multiple inheritance" ?