Let's say you quit iSRO. You join eSRO, you make 100 and full farm, have some fun but that's not enough. Then Bloody-Rose appear. What has Rose to offer? Something NEW, DIFFERENT. 11D, Alexandria, Forgotten World, Job Cave temple, but with some bugs that really bothers you, but since you have no alternative you keep playing. Then, Diamond appears, with pets fixed and customized content, you move there. One week later, ~10 more servers appear, some of them gives you 1kk(YES MILION) silk. You join that, you play Magic Pop until you full nova+9, then you realize that playing in a server full of, well, really retarded people, is a bad idea and a waste of time. You fulfilled your dream, you're full nova+9, you have all skills maxed out, you have more than 3 chars maxed out in everything. You see, after 1 month of playing on more then 5 servers, after achieving things you'll never achieve on isro, you get BORED. You get BORED because people don't PVP, people don't do job wars, people comes and goes doing the same thing over and over again, creating chars to fulfill their dream. Now, well, now you wait for Avalon's private 70 server with custom content to start, since it;s creator is a legit player and made the game for pvp/job war thing.
eSRO, Bloody and Diamond, and probably Zelos will resist.