Why aren't my Facebook ads consistent?

I’ve noted that whenever I run a Facebook ad to boost a post for a BookFunnel free giveaway, my click count is through the roof (at least for me) and are successful. (Normally in the 100-300 click count range for a $25 cost.)

However, if I boost a post for a sales BF promotion, even if it is KU, my click count drops to minimal levels in the 10-30 range for that same price. Am I doing something wrong or is it the nature of the beast?