dave2008
Legend
Actually the haven't been infinite since at least 4e.The planes are boring. Even Hell is boring. The problem is that planes are infinite, but we treat them as different mono flavors of Prime Material.
Hell is Lawful and Evil Prime. The Plane of Fire is hot and flickery Prime. The Feywild is Extra Prime and Shadowfell is faded, depressed Prime. You don't need an infinite space to be a BBEG lair.