Notice there are three copies of Verdant Catacombs and two copies of Scalding Tarn and Polluted Delta as the deck’s secondary “fetchlands.” This is due to the importance of finding green mana to cast Veil of Summer, which has more copies in the deck than Orim’s Chant.
For this reason, we prioritized building the mana base around the pairing of Underground Sea and Taiga. While white mana is nice, it comes secondary as it’s only needed on the combo turn and can always be cast off of Lotus Petal or Mox Opal. Every fetchland in the current iteration of TES cannot get one land, for Verdant Catacombs that land is Tundra. That said, it can still retrieve Scrubland as its white mana provider.
There’s more to Verdant Catacombs and the other fetchlands as well. They provide shuffle effects for cards like Brainstorm or Ponder which help with the quality of draws. Fetchlands protect TES’s mana from effects like Wasteland or Rishadan Port, which is key considering TES is a five-color deck with plenty of non-basic lands.