Because most of them are like angry sheep...eg, they can't or don't want to lead & know they couldn't survive alone, but still whine/chafe at being commanded. I side with Rick as well...If you don't like it, go away. If you stay, stop yer whinin'.

But mostly...the producers need to fabricate some drama, so that's what they do. lol
Edit: Rick's not Shane...he's just stopping the fantasy. Getting real, so to speak.