Isn't it obvious? A certain NPC from the other faction tries to "entice" you to their side, and this is a pure assumption but from what i have read its a good one. They have also said in a recent interview they plan on a free for all province where theres towns etc and any faction can go there. and i would like to further add no matter what faction you visit at level cap You will always fight for your original alliance in Cyrodiil this has already been stated

This is not WoW. In 50+ and 50++ you are trying to help those towns, not harm them.

Go PvP in Cyrodiil, it's far more satisfying slaying actual players than defenseless NPCs.

You can't see people of the home faction when you visit a 50+ so chill.

I never could understand why people like raiding towns and kill the king/leader or what have you. I guess it just goes to show the different age groups that play these games.