MarkB
Legend
Remember the scale of the galaxy. There are billions of stars. The relays skip over a few million stars to get to the next relay. Whole stellar empires could be nestled between the relays without anyone knowing the better... perhaps even the Reapers.
Another possibility: There could be several - even dozens - of different Relay networks, none connected to the others, all overseen by the Reapers, dozens of civilisations growing in parallel without ever touching each other.