[Gravedigger]

Likely David cleared the people out of that area, knowing that was where he was going to keep Ellie. Also...

Spoiler!

He said only a few knew of what they were doing with the bodies and that was the place in the game that Ellie saw them chop an arm off and put it into a bucket, so that's likely where they chopped up the bodies. I would imagine that David would only let people into the hall to eat and pray but they kick everyone out so they could butcher during off hours.