Yes, I've seen this too, and from what I can make out these are people who know about the 3 hour restriction (for example if they printed out their booking) and just don't notice the fairly large signs up about the trial. A few weeks ago I was chatting to a BA agent I know and someone came up to us, explaining his children were getting uncomfortable with the wait, and could he ask for a special favour to be allowed to check in early. The three of us were standing in front of the sign concerned, it was pointed out to him, the father was shocked he had spent an hour unnecessarily at the back of the hall.

Some people however are waiting for other people in their party to arrive (e.g. sorting out parking) and a few simply aren't prepared to use the machines, and would rather wait.