There are so many problems with PvP...that's why the maps are empty after two months. Game had so much potential...wish it was put out by an experienced company.
1. Using Siege equipment is boring.
2. Zerging is boring.
3. Everything in Cyrodiil is designed to encourage players to zerg and siege.
That's why everyone's leaving Cyrodiil. The funnest part of Cyrodiil is running around in a small group, looking for other small groups to fight. It's too bad that this doesn't contribute in any meaningful way to your alliance, nor is it easy to find other small groups since the game encourages players to join the zerg and tag along for easy kills/AP.