It is a little less confusing to me why audiences might not be as excited. It isn't what they came for. It means they have to sit for another "X" minutes before they can excape to the bar or the cigarette that is calling out to them or whatever.
But, with the proper frame of mind, talkbacks can be great for audiences too. Here's a lovely article on the pros of sitting for the talkback by Cara Joy David. It is also a good read for people who host talkbacks so they can see what works and why.
Many thanks to @NYCTheatreNews on twitter for sharing the link. FYI: they are a good follow. Follow them.