Even though they have "leadership", I actually think Rick and Shane make very poor leaders.
Neither of the two delegate duties, responsibilities or any form of discipline to the others. They come up with plans on their own, barely bothering to receive any input from the rest of the group, and both are too emotional about one thing or another.
Personally, I would probably make a better leader than both of them which is probably why the story chooses to focus on one defunct group instead of, let's say, that group of 30 that Randall is from - Which, for all we know, could run a better (perhaps a bit more violent and aggressive) crew than Rick and Shane's.
Something I've learned is that no matter how well disciplined or how well trained a group may be - It's ultimate enemy will be idleness.
Since Rick and Shane fail to give the group purpose/motivation, everyone just kind've mills about - doing whatever.