Hm, maybe you're right. But with Rebuild you want to buy Duchies after you have enough Rebuilds (two, IMO, sometimes three) so as the game goes on the density of Victory cards in your deck increases, it gets more likely that you end up drawing Victory cards you don't want to have in your hand. And it's not like he was playing just one Soothsayer at a time, he was playing multiple Governors for draw, further increasing the likelihood of having Victory cards you want to Rebuild forced into your hand.