Unless everyone knows everyone on a server, the "community" for each person on a server is something different and depends on the bonds that person made with other people. Like Gramul said, we're talking about huge spiderwebs here. If you have a small linkshell with 10 people and you consider the bonds every person has in that linkshell and want to get everyone who those people know to the same server and the ones they know... you'll probably end up dragging half if not the whole original server to the new one.
It's not just a matter of a few linkshells that need to move to the same server -_-