Maybe instead of waiting for the top tribes and same players to be able to join new worlds, they put out new worlds with the intention of possibly giving the "little" tribes a chance to win.
What I see being complained about on this subject has more to do with the lack of commitment of players rather than the developers. Players need to stay committed to whatever world they are fighting in regardless of whether a new world opens. While bigger tribes are fighting and staying committed to their current worlds, other tribes have a chance to gain a tribe following in a new world and maybe win. In the long run, that will create more competition anyway.
The way I see it, waiting for conflicts to end among the top tribes in previous worlds almost guarantees that those top tribes will always be winning worlds. And for the most part, the actual players that are winning are the same people that move from top tribe to top tribe. Is that fair? What about the "little" guys?