Why is this happening?
I've seen others taunting people: "I'll post XYZ picture if I get ## more followers!"
This is so completely backwards. Posting interesting content will cause people to want to follow you. Interesting content is not a weapon. It goes against everything organic about social media to use it to taunt people into following you. And those people are probably not going to return to your feed, so I hope you don't intend to ever use it to tell them anything else.
Twitter and Facebook followings are built over time, not crammed into one or two "follower drives." What sort of artificial timeline is making people do this all of a sudden??
Traditionally, marketing centered around "events" (hence Event Marketing). So, say, a book launch. A very clever marketer would arrange a series of appearances or reviews or other buzz-generating items slightly before, on, and after, a certain date.
Social media--the internet in general, really--is making Event Marketing a thing of the past. Which is not to say that it's not useful or that no one does it anymore. It still has its applications. But crafting an online presence is not meant to serve one date (although a good presence will give you a strong platform when there is a specific piece of info you need to disseminate). You have to create a reason for people to want to add you to the noise of the Interwebz, so make an effort. Followers drives ain't it.