I don't want to mention names because there are many. Most of them are probably coming from stake campaign. It seems like some of them are trying to make a post longer when it can be done with short post.
Do they get paid more for writing essays? I think it has more to do with merits than post quota for signature campaigns. Some believe long posts have higher chances of getting merits than concise and short posts. This belief did not come from thin air, there are members who reward long posts just because they feel the OP has put a lot of effort into writing a wall of text. Members who have been rewarded their ability to make long posts will find it difficult to change even as they grow in the forum.