As someone who's eaten many sauces and spice blends that incorporate Carolina reaper peppers, spiciness isn't the same as temperature with regard to heat. Lava's heat is physically destructive and one's tongue would likely be immediately burned beyond recognition. One wouldn't have time to assess the "taste" or texture at all before writhing in agony from severe burns.

In contrast, I can eat a hot sauce made from super hot peppers and, while I'm in agony from the extremely potent capsaicin in the peppers, I haven't damaged my tongue in the process so I can actually taste the flavor and detect the texture of the food.