it is because there are too many participants in the social media that's why the bounty funds is not enough to make a big payments to each participants, it is a verygood campaign and it is listed as the one of the very successful ico in july 2017.
Considering there were 84m(!) tokens reserved for social media bounty campaign, there should be more than 40K+ unique users, who participated both in Facebook and Twitter campaigns via TVE which seems at least unlikely or, better to say, IMPOSSIBLE. Yes, I put my 2000 earned tokens into calculations, but I'm sure there weren't a lot of social media tasks I missed as I started monitoring DENT TVE bounty campaign regularly even before a bounty thread on bitcointalk appeared.
So it's a big question where did those tokens go...