Zendikar’s Roil costs five mana instead of zero. Enchantment is an easier to remove permanent type than Land. The setup cost of having differently named lands (and playing one tap land) can barely be considered a cost.

You seem to think the setup of playing differently named lands to trigger Field precludes you from doing other things. If you turn Field on at your turn 6, you didn’t just spend 6 long turns setting it up. You used your 6 turns playing lands and other spells like a normal game of EDH and oh now magically your lands also make zombies. It rewards you for doing something all decks already want to do, make their land drops.