In correspondence type games, sometimes they don't know it's DAYS to move. They may be new to the site and just followed some link that said "click here to play chess" or something.
This was my experience many years ago on a different site. I started a few games, then noticed players had days to move, and I just abandon them without resigning or saying anything.
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In live games sometimes their connection is really bad. So they start a game, and it loads for you, but it's still loading for them, they don't even see the board yet. If it takes 5 or 10 seconds there's a good chance their opponent has already left, so they stop waiting and exit the site. This also explains why these people are trying for an unrated game -- they know their connection is bad. I've had this experience too recently, waiting for my ISP to fix things.
Sometimes when I start a game (this almost always happens with "Unrated" players), they never make their first move.
I usually don't win on time on games exept for these. If I'm white, I move, and they never move as black. If I'm black, no moves are ever made in the game because white won't move! It's getting to the point where this happens about every 3rd game I start! Eventually, when I notice that the person just never moves, I just abort the game (Sometimes they make their first move at the start, and never move on the second move, but very rarely, and I gain rating about 50% of the time on them losing on time).
This is getting very annoying on this site. And here's something even weirder; every single time this occurs, I click on their username and find out that I'm the ONLY one their playing! I don't understand why this occurs so often. Anybody out there have the answer?
Thanks