The big problem is that Data Center travel and some DCs being known for certain activities(Aether for raiding, Primal for PvP, Balmung exactly for ERP, etc) means that if you are a Dynamis character and want to do those things, the community encourages you to go to those DCs instead of staying in Dynamis, so even if Dynamis has a high enough number of raiders to sustain a population, it's never going to materialize because those raiders are all in Aether or Primal, it leads to a vicious cycle that is really difficult to break, and it isn't even truly SE's fault, they recent DC travel limitations were meant to discourage this behavior, but they just made inconvenient to play the game.

They'd have to do something to encourage raiding in your home DC, positive reinforcement over negative ones, but I couldn't tell you what that is.