How are you supposed to destroy another empire?
If you need 75% of the map to win with 30,000 provinces you need 22,500 provinces with 7,500 taken.
That means you have to destroy 2500 players to 3-province-empires. And no more than 2501 can play at the same time (for 8 months long).
And you still need a big alliance for alliance victories.. and some people really hate big alliances (or clans).