Maven `optional` module v. IntelliJ `export` module

When transforming a Maven project, IntelliJ doesn't use its Export module option to express a transitive dependendency. Why?

Consider this example:

POM project:

A --> B --> C

IntelliJ's interpretation:

A --> B --> C
  |
  --> C

instead IntelliJ could do this:

A --> (export) B --> (export) C

Why doesn't it?

A Maven POM file can declare an optional dependency.  So by default a Maven dependency is logically exported in IntelliJ parlance, but IJ doesn't materialize the project that way.