On Yom Kippur, the Kohen Gadol must be married to exactly one wife. We are also concerned about her passing away.
So the Gemara suggests that he gives a get to one wife on condition that the other doesn't die, and to the other on condition that he goes to Shul.
Why not just make a conditional marriage. Give a woman a ring "on condition" that the other wife will pass away on Yom Kippur, and then bring her into the house.
If the wife dies, the Kiddushin will work retroactively, and so will the Nissuin. If she stays alive, then there was no Kiddushin or Nissuin.
Seems much easier and fool proof.
Why didn't they do this instead?