I'm not saying everyone needed a significant number of lines. I'm saying that they seemed to have vanished into thin air. Heck, there wasn't even anyone visible in the background when Lori went outside. It was odd.
Why do you need to see every character every episode? In real life people don't need to see everyone they know in real life to know that they still exist. The other characters could simply be doing something unimportant, which is why the writers decided not to include them in the episode.
Do you need to see T-Dog make a five second appearance and say one line in every episode to be happy?