You'll notice there's three copies of Bloodstained Mire and only one Scalding Tarn as the deck's secondary "fetchlands." This is because the reliance on black mana is more important than blue. While this split may seem strange with ten one mana cantrips and only seven discard spells, keep in mind that cantrips are frequently sided out. In a format like Legacy, there's decks where you need to be able to cast discard on turn one and not worry about a Wasteland staring you down (I'm looking at you Death & Taxes and/or Delver decks). There's more to Bloodstained Mire and the other fetchlands as well, they provide shuffle effects for cards like Brainstorm or Ponder which help with the quality of our draws. Fetchlands protect our mana from effects like Wasteland or Rishadan Port, which is key considering TES is a deck with fewer lands than its other storm counterpart.