Well, normally projects would first create an ANN thread here on bitcointalk because its a forum full of people who knows about crypto and have the potential to buy in or invest on the project. (Although I would say that probably 90% of the members don't actually do) then a bounty campaign is initiated. If you were to share these projects on social media, it wouldn't gain much traction because not many know what crypto, coins, tokens etc. are. That was the case back in 2017 especially when ICOs were booming but I guess most projects are able to market better using other social media tools which turns out to be more effective for them, I believe.