As explained in its javadoc, purpose of Iterable is to support particular language syntax:

Implementing this interface allows an object to be the target of the "foreach" statement

As such, it belongs to lang package, which

Provides classes that are fundamental to the design of the Java programming language.

Other classes at the diagram belong to JCF and hence, are in util package which

Contains the collections framework...

As explained in its javadoc, the purpose of Iterable is to support particular language syntax:

Implementing this interface allows an object to be the target of the "foreach" statement

As such, it belongs to the lang package, which

Provides classes that are fundamental to the design of the Java programming language.

Other classes at the diagram belong to JCF and hence, are in the util package which

Contains the collections framework...