yeah, I was thinking it would be a good idea to go back to Crawford and just clear the place out
1. Its already fortified (probably some holes to fill, but most of the work is done)
2. They were the biggest bandit threat in the region, its likely they wiped out any other major threats in the region, so not many people to worry about.
3. Its already filled with supplies (even if the armory is empty, there should be guns lying around on dead bodies everywhere, + plenty of gas and working cars)
As for why do people keep moving, it depends on the situation, a lot of the time people have objectives, like Resident Evil, theres always some sinister time limit or someone is in danger and you have to get to them ASAP. In the living dead series, people actually hunker down as much as possible, like the original Dawn of the Dead and Day of the Dead. In Night of the Living Dead, the radio and TV announcements urges people to get to safe zones and out of their homes, thats why they wanted to move.
Generally theres 3 main reasons:
1. Finding loved ones.
2. Getting to somewhere safer.
3. Raiding supplies from town to town.
Now, in the game so far, you were at Hershel's farm with nowhere to go, so you went to Macon where your family is. You find out their fate and hunker down. Ep.2 you find a potentially safer area with more food, so you check it out. In Ep.3 your sanctuary is destroyed, so you have to leave.
In the short term, you could just find another area to settle in, but what about in 5 years when all your canned goods expire? Youre going to need to produce more food, thats why getting to an island gives you freedom to hunt, fish and plant new crops (assuming you find an island large enough). I think thats the idea with that.
In the case of where you are right now in the game, settling down in the house in Savannah is illogical, as theres no supplies there and even though its fortified, that house certainly isnt impenetrable.