Basically because :
1. It's new and fresh - not like grampy World of Warcraft. Of course take it easy :P ive had been playing WoW very long but i know very well Lotr and i think - LOTR is better and more interesting then WoW.
2. Have it's own charisma - ohh yes you can fall in love very fast.
3. I think world is better - Tolkien's Middle-earth is far more interesting then Azeroth. Yeah i know there is lots of Warcraft's books and other stuff- but hey read Lord of the Rings Trylogy!It's a classic!
4. Players in Lotr are nicer and when you are going somewhere, everyone is very helpful - WoW its different
5. You can purchase Lotr for lifetime membership in WoW you can't!
6. Traits, skills - they are far more efficient then in Warcraft.