You're forgetting about the Protheans. They began researching and developing Mass Effect Relays of their own. It's a central plot point in the first game.SajuukKhar said:It is a dead end path, the reapers made it so, the Asari's, and the other races in general, unwillingness to make new relays shows their dependance and their flawed civilization.
Eventually, Civilizations can begin to develop past the barriers the reapers set up. The entire idea is that the reapers are supposed to wipe out galactic civilization before they can use it. The reapers didn't realize the protheans had begun developing mass effect Technology before they invaded, that's what enable you to return to the Citadel in the first game.