Bitcointalk was popular some years ago, but for now not all cryptousers and crypto-intersted people know about the forum, so new projects don`t need to creat ANN thread, because for now only website and investors names are really important for listings and next development. Bitcointalk isn`t in priority now
Bitcointalk is still very popular platform and you will find many ANNs listed on it. Even though there are some project who do not advertise here but bitcointalk is not limited to the altcoins ANN. You will find that all the gambling sites prefer to have their ANN on this forum as they generate a lot of traffic from here.