Google has never been great at integrating their acquisitions. Even their own video search still can't seem to match YouTube's search for things on YouTube even with exact titles. Google Earth started as Keyhole. It's the K in KML. It gained notoriety pre-acquisition for being used in reporting on the invasion of Iraq. Maps was a different company.

You can export and import KML in Maps, but it's in a separate custom map interface under Saved->Maps. It's not integrated with the main interface like in Earth as far as I can tell. If there's a way to load them like overlays in Earth, that would be useful.

Last I knew, Google Earth on desktop also lets you play with local KML files.