It's necessary for me, for a new coin every publicity small or big should be considered, the coin has a huge potential for them not to need Bitcointalk for their announcement, Bitcointalk is a big publicity site, all discussions here are indexed in the search engine and open to all potential visitors, all I know they don't want to be criticized if they do not want to open a thread here.
And you know what, even the best projects have had the time to create an announcement thread, giant altcoins such as Ethereum also created topic and announced their project. I don't know why any project would not want all the possible attention and investors they can get by just dedicating a few minutes of their by creating a thread.
They are just unaware about the existence of Bitcointalk forum should be the only logical explanation. Bitcointalk and telegram channels are the only medium through which they communicate with the community because FB, Twitter are meant for announcements rather than discussions and for any project to gain investors and interest, they must communicate with the potential investors.