The rehashed SNES maps are entirely new, they just have the same overhead layout as the SNES tracks. Saying they rely on nostalgia—yeah, that's true. Saying that it's laziness? No, it's no simpler than making a new track from scratch. Probably harder, given they have to make it work with the existing layout, despite the pace and physics being so different.
Anything more reliable than Nintendo resorting to laziness and calling upon nostalgia?