Bottom posters just love to scroll down for *every* message instead of using their page down button or simply clicking on the next message to see something new.
Bottom posting became popular when the mouse scroll wheel was invented... one justifies the other.
Bottom posters don't like to use a split screen to display message contents since the space available is never enough to get them past the stuff they've already read before.... they open each message to the entire screen so that they have half a chance of seeing the response (at the bottom of the message of course).
Bottom posters have such a short memory that they didn't remember what they just read one posting ago and like to see it all over again or don't like to move one post up to see previous contributions.
On an emotional side, bottom posters love the suspense waiting for the new response to show up while they are scrolling feverishly downward. They would never cut, edit or abbreviate previous information to make their response shorter. This would shorten the anticipation while searching for the new contribution. Why read the readers digest version when you can have it all?
If they can't use their scroll wheel to get to the nugget of new info, the bottom poster doesn't feel fulfilled!
TOP POSTERS UNITE! Do post on the top! Do edit out repetitious information, or leave only the bare minimum required for continuity BELOW your new information (as a courtesy)! Be helpful to all the other readers so they can see the new information or response with no further fuss, delay, or effort. The biggest way to frustrate bottom posters is to give them the information up-top so that the bottom poster doesn't have to scroll or anticipate! WE SHALL PREVAIL!