What could be the reason for this ?
If that's actually really the case, I'm guessing that some projects simply just has too much publicity right off the bat on social media that the publicity for posting on Bitcointalk might be quite irrelevant. Especially when a certain project isn't planning on having a bounty campaign, they might not get that much traction here at all.
I agree because some of the projects are focused on social medias whein millions to billions of audiences get advertised every single day plus the streaming sites. Youtube, twitter, facebook, telegram, reddit are common to newer projects nowadays.