Objects know about things they are derived from, all the way back to object - but no class should know about anything that is derived from it.
So if ClassA derives from ClassB, and ClassC derives from ClassA, then:
ClassC can use anything in ClassA or ClassB
ClassA can use anything in ClassB, but nothing from ClassC
ClassB cannot use anything from ClassA or ClassB
Extending that to language packs - everything derives from Object - but that means Object cannot access anything in any other class. So how could java.lang import "every other class" that could possibly be created and derived from Object?
java.lang contains just the basics - stuff nearly every program is going to need - it does not contain "specialised classes" that are imported from their own packages: java.lang (Java SE 11 & JDK 11 )