I was doing work with Epic and other game developers on UE3 when they changed from the Terrain actor to the Landscape actor.
I wrote most of the UDN documentation on both of those actors for that engine and for 2.5.
There was a lot of outcry from most of the licensees regarding the design and functionality of Landscape.
And numerous promises by Epic to make some of the design issues right.
I had hoped that with UE4 they would have revisited Landscape and actually fixed a lot of it up.
It was probably just left as-is between engines because no one wanted to take it on.