Then they could exist on far fewer planets.
How can we retcon it as realistic? The problem is a typical star can only have perhaps 2 planets in a comfortable temperature zone. Moore says he imported the idea of the colonies - 12 colonies at one star system - from the original series, knowing that this is not actually realistic. It seems very harsh, but it does have a food source. This planet may not be strictly habitable. It is also exciting for being somewhat hidden. This discovery elicits great excitement both as the first such planet seen, even though it is barely habitable. Of course, Kobol is not a new, undiscovered planet.
Depending on fuel available, I presume that means scanning thousands of planets. As the fleet moves through space, it is regularly sending out scouting missions in Raptors, searching for food, resources and fuel.
In the BSG universe, it looks like nice planets are rare.