It's easy to understand why in TNG, because everyone is wearing a combadge and the computer would detect the movement of the entire ship population. For the crew, you assume that people have shifts that are logged with the computer system. When a crew member leaves their quarters and is scheduled to appear at a certain post at a particular time, you'd figure that the computer would sent a turbolift to their location or cause one traveling past to pause for him/her to get on board.
However, this is all a rather pointless exercise. Unless there would be a story element involved where two crew members need to have a dialog in semi-seclusion that would then be suddenly interrupted by someone appearing, like having them wait at a turbolift, there's no need to show people waiting for one. Thus, we are not shown it, when it's quite possible that turbolift queues happen all the time. We just don't get to see them
. I think that's the simplest explanation.