Hmm well now that is interesting. I wonder what made them decide to change it? They should re-examine this idea for the next Mario Kart game after this one (Mario Kart 9?). That could give them a new take on the lava courses like Bowser’s Castle for example since if you were to drill into the core of the Earth you find magma. Granted that doesn’t necessarily mean the Mushroom Kingdom has magma beneath the surface, but even so. Plus they could even bring back the Super Mario Bros. themed underground levels and make a track based around that concept.
Source: DidYouKnow Gaming