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...they are mostly done to qualify for the signature campaign. campaign managers mostly count long posts. because they look high quality.
Campaign managers who rely on long posts to pick campaign participants are like managers who look at earned merit of users in making their picks. If someone writes a long (and expectedly, boring) post on page one, there's a chance that it gets read unlike when that same post is on page 10 or on a mega thread. These are some of the little things that should mean something. Most times, these lengthy posts don't make much sense like the two-three liners and they get passed over more. What's the essence of making posts others don't bother to read?
I ask myself same question too, why make a lengthy post people won't bother to read? Then it occurred to me that a particular topic can interest someone so much that he carefully analizes each point he makes so well that whoever stumbles on the post will be glad he read the writeup. Most time it is not all about seeking for merits, validation from campaign managers or even seeking for attention. You can be so vast in a particular topic that you'll be surprised at the whole stuff you've written.
Another thing is the timing of your post. A lengthy post can actually be noticed in the first two pages. Making a lengthy post on a 15th page sounds like a joke to me, especially now we have lots of lazy readers around, the possibility of the post being skipped by many is high.