Of course Bitcointalk is not the only one forum related to Bitcoin and cryptocurrency. There are a lot of forums like Bitcointalk, they also have marketplace and campaign like in here but the payrate is really low and the number of member in these forums is low as well so I think Bitcointalk.org still the best forum about cryptocurrency for now 
I agree with you that there are very many forums such as bitcointalk. But still the best is this forum, see that in other forums we can not get the liveliness of such discussions. In bitcointalk we can discuss with many people, looking for information about bitcoin. Here there are many people who influence the development of bitcoin. So you do not worry when you do not know something because all the users here will help you. I am very confident that everyone in the world who knows bitcoin at this time then they also must know this forum.