UMLR — Including use case depends on included use case but Include is no subclass of Dependency

The following sentences of the specification made me wonder why Include is no subclass of Dependency.

"As the primary use of the Include relationship is for reuse of common parts, what is left in a base UseCase is usually not complete in itself but dependent on the included parts to be meaningful. This is reflected in the direction of the relationship, indicating that the base UseCase depends on the addition but not vice versa."

Instead of the dependency being reflected in the direction of the relationship, the class could explicitly have Dependency semantics.