Zombies simply doesn't have the quantity of good creatures to make curving out into a lord or two a better strategy than playing a better non zombie in the place of lords
The problem is that there were five of them, and all five had extremely limited uses
Sultai Reanimator Through the Omen Paths hasn't had much impact on Standard, but it does have a four mana sorcery-speed reanimation effect, Kavaero, Mind-Bitten, and that's proven mighty enough to fuel an entire strategy
Ramp that is good for cycling decks is hard to come by
whenever you cast a noncreature spell you dont own, you get two Treasure tokens to use later
However, Magic players have never really had a good incentive to build a deck with more than 60 cards outside of Battle of Wits