I think the Maze itself is suited to be a land, just because the name evokes a "location", as a land should be. The ability is a bit more vague; I could see it being a land as it was probably intended to "confuse" the creature, being in a Maze and all.
So maybe it does come down to flavor also. Oasis "heals" creatures, being a resting point in a Desert. Desert causes damage, being presumably in a "sandstorm"... I guess further research would actually have to go into finding lands where their ability doesn't fit the "flavor" of being a land (not sure of the background of Sorrow's Path and the switching of blockers, for example).