The rock saw is sweet, but having to wait until you attack, and only being able to hit artifacts, and giving your opponent a free card is less sweet
For instance, take a look at Sultai Charm: Charms have always been popular cycles, and the gold ones have pretty classically excelled at showing up in Constructed
This Spider untapping after you cast a big spell can assist you with chaining more of them together as the game goes on
Forcefield ($600) Forcefield is a card that can find some use to keep you alive, particularly against big creatures swinging at you
Theres a lot of redundancy there to make this card behave right
But the Wellspring offers white significant and easily obtainable card advantage, which means its more needed than the other cards