When the time for upgrades does come, there are a variety of products to choose from that will provide you with new cards, either through additional play experiences or through the unique thrill of unwrapping brand new booster packs
By comparison, an equipment deck doesnt feel all that unique (case in point: The Final Fantasy Starter Kit has an equipment deck with the same exact color combination)
You can do this at instant speed, letting you sneak some damage through your opponents who might not be paying attention to your open mana, and very likely, not to the abilities you have tacked on those lands
The damage can add up, and be enough to sometimes even wipe the entire board of creatures depending on the gamestate
Tortured Existence trades creatures between hand and graveyard, Frantic Search loots and untaps lands so you can keep mana up, and Reanimate just grabs the real thing when needed
Many energy cards are primarily designed to be one or the other, and exploiting the differing rates of returns between them using the efficient generators to fuel the powerful outlets is a big part of deckbuilding around this mechanic
