they are allocating more tokens on social media campaigns because so many participants join, even you won't find big allocation to signatures, manager just wants to do justice to all campaign participants, even though it looks unfair to signature participants
There are fewer signature campaign participants, so even though the allocation is smaller than social media campaigns, most of the signature campaign participants get more tokens from social media campaign participants. if possible then join as many campaigns as you can handle, it's better if we join signature and social media campaigns 
That's where it's important to understand and read the rules well. if we feel it's not fair enough then it's better not to join, simple right? every BM must also always remind that whatever the risk, the bounty hunter must be ready to accept.