For me I would say because of its diversity. I have been a member of the altcointalk community for quite some time now and during some discussions there I noticed that some altcointalk users are always mentioning Bitcoin talk so I decided to create an account here to see how it really looks like and to be sincere since I have been here even if I'm not that active here I can boldly say that all the features that were mentioned in altcointalk about bitcointalk is just so correct. Here you have users that have a vast knowledge about Bitcoin and some of them have been around since the creation of Bitcoin. all those out together are some of the reasons why I'm here today at bitcointalk.