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 am quite curious though, when people talk about cryptocurrency and where there is a place that it will be known by a lot of people then it would surely be here, the Bitcointalk forum.
In social media, I don't know how would people would even care about a certain crypto-related projects.
If it is somehow related to popular companies like Microsoft, I guess it would still be reasonable to use other social media sites.